Filter media having a fine pore size distribution

ABSTRACT

Filter media having a relatively small pore size and related components, systems, and methods associated therewith are provided. The filter media may include a fibrous efficiency layer, a fibrous support layer, and a third layer adjacent to the efficiency layer. The efficiency layer may impart a relatively homogeneous pore structure to the filter media without adding substantial bulk to the filter media. The support layer may promote the homogeneity of the pore structure. For example, the support layer may prevent and/or minimize defects in the relatively thin efficiency layer that may result from manufacturing and/or processing. The third layer may serve to impart beneficial filtration (e.g., efficiency, dust holding capacity) and/or non-filtration (e.g., layer protection) properties to the filter media without adversely affecting one or more properties of the filter media. Filter media, as described herein, may be particularly well-suited for applications that involve liquid filtration, amongst other applications.

FIELD

The present embodiments relate generally to filter media and,specifically, to filter media having a relatively small pore size whichmay be used in a variety of applications (e.g., liquid filtration,removal of small particulates).

BACKGROUND

Filter elements can be used to remove contamination in a variety ofapplications. Such elements can include a filter media which may beformed of a web of fibers. The fiber web provides a porous structurethat permits fluid (e.g., gas, liquid) to flow through the media.Contaminant particles (e.g., dust, floccules, precipitates, organicmatter, mineral or metallic oxides, micro pollutants, microorganismparticles, virus particles, biological cells, debris from biologicalcells, and biomolecular aggregates) contained within the fluid may betrapped on or in the fiber web. Depending on the application, the filtermedia may be designed to have different performance characteristics suchas enhanced particulate efficiency. Fiber web characteristics (e.g.,pore size, fiber dimensions, fiber composition, basis weight, amongstothers) affect filtration performance of the media. Although differenttypes of filter media are available, improvements are needed.

SUMMARY

Filter media having a relatively small pore size and related components,systems, and methods associated therewith are provided. The subjectmatter of this application involves, in some cases, interrelatedproducts, alternative solutions to a particular problem, and/or aplurality of different uses of structures and compositions.

In one set of embodiments, filter media are provided. In oneembodiments, a filter media comprises a first fiber web comprising firstfibers having an average diameter of less than or equal to about 0.5microns and a thickness of less than or equal to about 200 microns; acalendered fiber web directly adjacent to the first fiber web; and athird fiber web bonded to the first fiber web, wherein the filter mediahas a maximum pore size of greater than or equal to about 0.1 micronsand less than or equal to about 2.5 microns and a full width at halfmaximum of a pore size distribution of less than or equal to about 0.2microns.

In another embodiment, a filter media comprises a first fiber webcomprising first fibers having an average diameter of less than or equalto about 0.5 microns and a thickness of less than or equal to about 200microns; a calendered fiber web directly adjacent to the first fiberweb; and a third fiber web bonded to the first fiber web, wherein thefilter media has a maximum pore size of greater than or equal to about0.1 microns and less than or equal to about 2.5 microns and a ratio ofmaximum pore size to mean pore size of less than or equal to about 5.0.

In one embodiment, a filter media comprises a first fiber web comprisingfirst fibers having an average diameter of less than or equal to about0.5 microns and a thickness of less than or equal to about 200 microns;a second fiber web directly adjacent to the first fiber web, wherein thesecond fiber web has a dry tensile strength in the machine direction ofgreater than or equal to about 1 lb/in and less than or equal to about35 lb/in, a dry tensile elongation in the machine direction of greaterthan or equal to about 10% and less than or equal to about 60%, and amean pore size of greater than or equal to about 1 micron and less thanor equal to about 30 microns; and a third fiber web bonded to the firstfiber web, wherein the filter media has a maximum pore size of greaterthan or equal to about 0.1 microns and less than or equal to about 2.5microns, and a full width at half maximum of a pore size distribution ofless than or equal to about 0.2 microns.

In another embodiment, a filter media comprises a first fiber webcomprising first fibers having an average diameter of less than or equalto about 0.5 microns and a thickness of less than or equal to about 200microns; a second fiber web directly adjacent to the first fiber web,wherein the second fiber web has a surface mean pore area of greaterthan or equal to about 2 μm² and less than or equal to about 50 μm², anintersection density of greater than or equal to about 0.005intersections/μm² and less than or equal to about 0.025intersections/μm², and a mean pore size of greater than or equal toabout 1 micron and less than or equal to about 30 microns; and a thirdfiber web bonded to the first fiber web, wherein the filter media has amaximum pore size of greater than or equal to about 0.1 microns and lessthan or equal to about 2.5 microns, and a full width at half maximum ofa pore size distribution of less than or equal to about 0.2 microns.

In another set of embodiments, methods of forming a filter media areprovided. In one embodiment, a method of forming a filter mediacomprises bonding a layer to at least a portion of a surface of a firstfiber web to form a filter media, wherein the first fiber web has amaximum pore size of greater than or equal to about 0.1 microns and lessthan or equal to about 2.5 micron and a ratio of maximum pore size tomean pore size of less than or equal to about 5.0, wherein the firstfiber web is directly adjacent to a second fiber web, and wherein themaximum pore size of the filter media is within about 0% to 100% of themaximum pore size of first fiber web prior to the bonding step.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1A shows a cross-section of a filter media according to certainembodiments;

FIG. 1B shows a cross-section of a filter media according to certainembodiments;

FIG. 1C shows a cross-section of a filter media according to certainembodiments;

FIG. 2A is a scanning electron microscopy (SEM) image of an uncalenderedfiber web according to certain embodiments;

FIG. 2B is an SEM image of a calendered fiber web according to certainembodiments;

FIGS. 3A-3D show plots of (A) average (mean) pressure drop at 15 litersper minute (lpm), (B) mean 0.2 micron particle efficiency, (C) mean dustholding capacity (DHC) at 2 bar, and (D) mean 0.3 micron particleefficiency of various filter media, according to certain embodiments:

FIG. 4 is a plot of the 0.2 micron particle efficiency of various filtermedia in flatsheet (disk) and cartridge (element) configurations,according to certain embodiments; and

FIG. 5 is a plot of the dust holding capacity (DHC) (also referred toherein as dirt holding capacity) of various filter media in flatsheet(disk) and cartridge (element) configurations, according to certainembodiments.

DETAILED DESCRIPTION

Filter media having a relatively small pore size and related components,systems, and methods associated therewith are provided. The filter mediamay include a fibrous efficiency layer, a fibrous support layer, and athird layer adjacent to the efficiency layer. The efficiency layer mayimpart a relatively homogeneous pore structure (e.g., narrow pore sizedistribution, low maximum pore size to mean pore size ratio) to thefilter media without adding substantial bulk (e.g., thickness, basisweight) to the filter media. The support layer may promote thehomogeneity of the pore structure. For example, the support layer mayprevent and/or minimize defects in the relatively thin efficiency layerthat may result from manufacturing (e.g., of the efficiency layer)and/or processing (e.g., bonding, winding, pleating, slitting). Thethird layer may serve to impart beneficial filtration (e.g., efficiency,dust holding capacity) and/or non-filtration (e.g., layer protection)properties to the filter media without adversely affecting one or moreproperties of the filter media. Filter media, as described herein, maybe particularly well-suited for applications that involve liquidfiltration, including microfiltration and ultrafiltration in sterileenvironments, though the media may also be used in other applications,such as microfiltration and ultrafiltration for the oil and gas, processwater, wastewater, municipal, semiconductor, food, desalination, andchemical industries.

Filter media including a low basis weight and/or thin efficiency layerwith a relatively small and homogeneous pore structure may beadvantageous in many applications. Such filter media may have porecharacteristics that efficiently capture small particles (e.g.,colloidal aggregates, suspended organic and inorganic matter) whileallowing fluid to pass through with relative ease. The low thicknessand/or basis weight of the efficiency layer may reduce the impact of thetight pore structure on pressure drop, allowing, at least in part, thefilter media to have a relatively low pressure drop. The low pressuredrop may result in improved energy efficiency, relatively long lifetime,and/or reduced likelihood of damage to the filter media duringoperation. In addition, the thinness of the efficiency layer, andaccordingly the filter media, may allow more filter media to fit into astandard filter element resulting in an increased effective filter areacompared to thicker filter media. In some instances, the relativelysmall and homogeneous pore structure may be formed using fibers havingrelatively small diameters (e.g., less than or equal to about 0.5microns). The relatively small diameter fibers and uniformity of fiberdiameter (e.g. coefficient of variation around 30%) may impart arelatively higher surface area to the efficiency layer, resulting in agreater particulate capturing efficiency for a given basis weight.Without being bound by theory, it is believed that fine fibersfacilitates a smaller pore size in an efficiency layer, and uniformityin fiber size facilitates a narrow pore size distribution. Further,without being bound by theory, the absence or minimization of fibermerging and bundling is conducive to the formation of smaller pores.

However, low basis weight and/or thin efficiency layers may bemechanically fragile. In some cases, the smaller the basis weight,thickness, and/or fiber diameter of the efficiency layer, the lower thestrength of the efficiency layer. The fragile nature of the efficiencylayer tends to result in defects that adversely affect the homogeneityof the pore structure. These defects can occur, e.g., during formationof the efficiency layer or later on in the filter media or filterelement manufacturing process. As a result, low basis weight and/or thinefficiency layers in conventional filter media may display significantvariation in the pore sizes across the area of the filter media that maysignificantly reduce the filtration efficiency of the filter media.Accordingly, some conventional filter media utilize thicker efficiencylayers, which produce thicker filter media. The thicker efficiencylayers may suffer from a relatively high pressure drop, short lifetime,reduced energy efficiency, and/or reduced effective filter area. Thereis a need for filter media including a low basis weight and/or thinefficiency layer with a relatively stable, small, and homogeneous porestructure

The filter media, described herein, includes a low basis weight and/orthin efficiency layer that does not suffer from one or more limitationsof conventional filter media. In some embodiments, as described in moredetail below, the filter media includes a fibrous support layer havingone or more properties that serve to promote the formation of and/orprotect the integrity of fiber webs having relatively small pore sizesand/or homogeneous pore structures. For instance, the fibrous supportlayer may have surface properties (e.g., pore size, solidity,smoothness, fiber intersection density, surface mean pore area) thatfacilitate efficiency layer (e.g., fiber web having an average fiberdiameter of less than or equal to about 0.5 microns) formation withoutsignificant deformation of the deposited efficiency layer within thepore area of the fibrous support layer, and/or may have mechanicalproperties (e.g., tensile strength, tensile elongation) that sharplyreduce the amount of stress imparted to the efficiency layer, e.g.,during manufacture, handling, and/or application. For example, withoutbeing bound by theory, it is believed that a support layer having asmall surface pore area and/or a relatively smooth surface can minimizethe average bridge length (e.g., length of fiber between two solidportions of the support layer that is not in direct contact with a solidportion of the support layer) of the fibers in the efficiency layer. Incertain embodiments, the support may prevent defects during the filtermedia and/or filter element manufacturing process. For example, thesupport layer may prevent defect formation during manufacturing steps,such as during bonding (e.g., adhesively, via lamination) of theefficiency layer to another layer (e.g., fiber web, third layer).Without being bound by theory, it is believed that dimensional stabilityof the support layer reduces the amount of strain of the nanofiber webduring processing and handling steps. Calendering may increase thesolidity and/or the dimensional stability (e.g. increased strength,increased toughness, increased compressive modulus) of a fiber web(e.g., polymer fiber web) to be used for, e.g., a support layer. Withoutbeing bound by theory, it is believed that calendering can increase theamount of bonding between individual fibers in the fiber web (e.g.,polymer web) and also increase the amount of crystallinity of thepolymer in embodiments where the fiber web comprises polymer fibers,both of which may result in higher strength and toughness.

Regardless of whether defect formation is prevented or otherwiseminimized during the web formation and/or subsequent manufacturingsteps, a low basis weight and/or thin efficiency layer adjacent to(e.g., directly adjacent to) the support layer described herein may havea relatively small and homogeneous pore structure when incorporated intoa filter media and/or filter element. For instance, a support layer,described herein, directly adjacent to a low basis weight and/or thinefficiency layer comprising relatively small fibers (e.g., averagediameter of less than or equal to about 0.5 microns) allows theefficiency layer or a plurality of such efficiency layers to withstandprocessing conditions that would otherwise typically result in increasedpore size and/or defects (e.g., fiber web formation, bonding with otherlayers, tension from rollers). As an example, a fibrous efficiency layerdirectly adjacent to the support layer may substantially retain the porestructure when bonded to a third layer (e.g., protective layer) usinglamination (e.g., heat lamination) or an adhesive (e.g., an acrylicadhesive, an acrylic copolymer adhesive) whereas a similar process usinga conventional support layer may result in a significant change in porestructure. In some embodiments, filter media described herein aresubstantially free of an adhesive. In some embodiments, filter mediadescribed herein have no adhesive.

Filter media described herein may be used in a variety of applications(e.g., liquid filtration. e.g., removal of fine small particulates anddust when filtering microelectronic fluids, paints, solvents, otherchemicals, water, food or biopharmaceutical suspensions).

Non-limiting examples of filter media described herein are shown inFIGS. 1A-C. In some embodiments, as illustrated in FIG. 1A, a filtermedia 100 may comprise a first fiber web 102. Fiber web 102 may be afibrous efficiency layer having a relatively small and homogeneous porestructure. For instance, fiber web 102 may have a relatively smallmaximum pore size (e.g., less than or equal to about 2.5 microns, lessthan or equal to about 1.5 microns, less than or equal to about 1.0microns) and/or mean flow pore size (e.g., less than or equal to about1.0 micron, less than or equal to about 0.4 microns). In some instances,the ratio of maximum pore size to mean pore size of the first fiber webmay be less than or equal to about 5 (e.g., less than or equal to about2.7). Fiber web 102 may have a relatively narrow pore size distribution.For instance, the first fiber web may have a full width at half maximumof a pore size distribution of less than or equal to about 0.2 microns(e.g., less than or equal to about 0.1 microns).

Fiber web 102 may be relatively thin and/or lightweight. For instance,the first fiber web may have a thickness less than or equal to about 200microns (e.g., less than or equal to about 20 microns). In some cases,the first fiber web may have a basis weight of less than or equal toabout 10 g/m² (e.g., less than or equal to about 5.0 g/m², less than orequal to about 2.0 g/m²). In some embodiments, the first fiber web maycomprise fibers having a relatively small diameter. For example, fiberweb 102 may comprise fibers having an average diameter of less than orequal to about 0.5 microns (e.g., less than or equal to about 0.2microns). In some such cases, first fiber web 102 may comprisecontinuous fibers (e.g., electrospun fibers) having an average diameterof less than or equal to about 0.5 microns.

Filter media 100 may also comprise a support layer. The support layermay comprise a second fiber web 104 adjacent to first fiber web 102. Insome such embodiments, first fiber web 102 may be formed onto secondfiber web 104. The second fiber web 104 may have one or more surfaceand/or mechanical properties that promote the homogeneity of the porestructure of first fiber web 102. For instance, the surface mean porearea of second fiber web 104 may be less than or equal to about 50 m²′(e.g., less than or equal to about 25 μm²). As used herein, the term“surface mean pore area” refers to an average pore cross-sectional areaat a surface of a layer, e.g., comprising a fiber web. This surface meanpore area may be determined by analyzing a scanning electron microscopy(SEM) image as described further herein. The root mean square surfaceroughness of the second fiber web 104 may be less than or equal to 12 μm(e.g., less than or equal to 6 μm). In some instances, second fiber web104 may have a tensile strength of less than or equal to about 35 lb/in(e.g., less than or equal to about 30 lb/in) in the machine directionand/or a tensile elongation of greater than or equal to about 10% andless than or equal to about 60% in the machine direction. In someinstances, second fiber web 104 serves to promote and/or otherwisemaintain the homogeneity of first fiber web 102 by decreasing the stresson the first fiber web 102 during fabrication and/or use of the filtermedia 100. In some embodiments, third fiber web 106 is a meltblownlayer. In some embodiments, third fiber web 106 has an average fiberdiameter greater than that of the first fiber web 102 and less than thatof the second fiber web 104.

In some embodiments, calendering (e.g., smooth roll calendering) may beused to impart one or more beneficial surface and/or mechanicalproperties to the second fiber web. For instance, calendering mayincrease the smoothness, strength, and/or solidity of the second fiberweb while decreasing the surface mean pore area, the amount of surfaceprotruding fibers, and/or the amount of loose fibers on the surface ofthe support layer. The second fiber web may be calendered prior tocontact with the first fiber web. In some such cases, filter media 100comprises a first fiber web that is not calendered and a calenderedsecond fiber web. In some embodiments, one or more beneficial surfaceand/or mechanical properties may be imparted to the second fiber web viaa non-calendering process. For example, fiber selection may be used toimpart beneficial properties to the second fiber web. In certainembodiments, second fiber web 104 may comprise continuous fibers (e.g.,meltblown fibers). In certain embodiments, second fiber web 104 may be awetlaid or non-wet laid fiber web comprising staple fibers (e.g. Cyphrexfibers, Lyocell fibers, glass fibers, fibrillated fibers) having arelatively small diameter and/or a relatively small length, which maydecrease the pore size of the second fiber web, and staple fibers havinga relatively large diameter.

Filter media 100 may further comprise a third fiber web 106. The thirdfiber web 106 may be configured to impart beneficial properties (e.g.,dirt holding capacity, abrasion protection) to the filter media whilehaving relatively minimal or no adverse effects on one or moreproperties of the filter media that are important for a givenapplication. In some embodiments, the third fiber web serves as aprotective and/or capacity layer (e.g., pre-filter layer). For instance,the third fiber web may serve to capture and retain particulates (e.g.,coarse particles) during filtration thereby enhancing the dirt holdingcapacity of the filter media and/or prevent abrasive damage and othercontact induced damage to one or more layers (e.g., efficiency layer) ofthe filter media. In other embodiments, the third fiber web may be anefficiency layer. In some such embodiments, the third fiber web may haveone or more properties (e.g., pore size, basis weight, thickness) thatis/are substantially similar to and/or the same as a property of thefirst fiber web.

Regardless of the function of the third fiber web, third fiber web 106may be bonded to first fiber web 102. In some embodiments, the thirdfiber web may be bonded to the first fiber web via a lamination process(e.g., heat lamination). In certain embodiments, the third fiber web maybe adhesively bonded to the first fiber web. It should be understoodthat in some conventional filter media, the bonding process between theefficiency layer and another layer may damage the structure of theefficiency layer in a manner that increases the maximum pore size (e.g.,due to defect formation) and/or pore distribution. However, anefficiency layer (e.g., first fiber web) adjacent to the support layer(e.g., second fiber web) described herein does not experience the damagetypical of conventional filter media. Additionally, the third fiber webcan act as a pre-filter to the efficiency layer resulting in higheroperation life-time of the efficiency layer. In some embodiments, thethird fiber web has a maximum pore size below 70 microns; a soliditybetween 5% and 50%, and/or a basis weight between 5 g/m² and 50 g/m².

In some embodiments, the filter media may comprise one or moreadditional layers as illustrated in FIGS. 1B-1C. For instance, asillustrated in FIG. 1B, a filter media 120 may include a first fiber web122 (e.g., efficiency layer), a second fiber web 124 (e.g., supportlayer), a third fiber web 126, and a fourth fiber web 128. In certainembodiments, third fiber web 126 may be part of the efficiency layer.That is, the efficiency layer may comprise first fiber web 122 and thirdfiber web 126. In such cases, fourth fiber web 128 may be a protectivelayer. In some such cases, fourth fiber web 128 may be adjacent (e.g.,directly) to third fiber web 126. Third fiber web 126 may be bonded(e.g., directly) to first fiber web 122 and fiber web 122 may beadjacent to second fiber web 124 as illustrated in FIG. 1B. In someembodiments, third fiber web 126 is a meltblown layer. In someembodiments, third fiber web 126 has an average fiber diameter greaterthan that of the first fiber web 122 and less than that of the fourthfiber web 128. In some embodiments, third fiber web 126 has an averagefiber diameter less than that of the second fiber web 124.

In other embodiments, the fourth fiber web may not be adjacent (e.g.,directly) to the third fiber web. For instance, as illustrated in FIG.1C, a filter media 140 may include a fourth fiber web 146 adjacent(e.g., directly) to a second fiber web 144. In some such cases, secondfiber web 144 and fourth fiber web 146 may be part of the support layer.That is, the support layer may comprise second fiber web 144 and fourthfiber web 146. In some cases, second fiber web 144 may have one or moreproperties that promote the homogeneity of the first fiber web (e.g.,efficiency layer) and/or fourth fiber web 146 may provide beneficialmechanical properties to the filter media. First fiber web 142 may beadjacent (e.g., directly) to and/or bonded to third fiber web 148.

In some embodiments, all layers (e.g., fiber webs) in the filter media(e.g., filter media 100, filter media 120, filter media 140) are non-wetlaid.

As used herein, when a fiber web is referred to as being “adjacent”another fiber web, it can be directly adjacent the fiber web, or anintervening fiber web also may be present. A fiber web that is “directlyadjacent” another fiber web means that no intervening fiber web ispresent.

In general, the one or more additional fiber webs may be any suitablefiber web (e.g., a scrim fiber web, a backer fiber web, a substratefiber web, an efficiency fiber web, a capacity fiber web, a spacer fiberweb, a support fiber web).

In some embodiments, one or more fiber webs in the filter media may bedesigned to be discrete from another fiber web. That is, the fibers fromone fiber web do not substantially intermingle (e.g., do not intermingleat all) with fibers from another fiber web. For example, with respect toFIG. 1, in one set of embodiments, fibers from the first fiber web donot substantially intermingle with fibers of the second fiber web.Discrete fiber webs may be joined by any suitable process including, forexample, lamination, thermo-dot bonding, calendering, through-gasbonding, ultrasonic processes, chemical bonding process (e.g., to formcovalent bonds), or by adhesives, as described in more detail below. Itshould be appreciated, however, that certain embodiments may include oneor more fiber webs that are not discrete with respect to one another.

It should be understood that the configurations of the fiber webs shownin the figures are by way of example only, and that in otherembodiments, filter media including other configurations of fiber websmay be possible. For example, while the first, second, and optionalfiber webs are shown in a specific order in FIG. 1, other configurationsare also possible. For example, an optional fiber web may be positionedbetween the first and second fiber webs. It should be appreciated thatthe terms “first”, and “second” fiber webs, as used herein, refer todifferent fiber webs within the media, and are not meant to be limitingwith respect to the location of that fiber web. Furthermore, in someembodiments, additional fiber webs (e.g., “third”, “fourth”, “fifth”,“sixth”, or “seventh” fiber webs) may be present in addition to the onesshown in the figures. It should also be appreciated that not all fiberwebs shown in the figures need be present in some embodiments.

As noted above, filter media, described herein, may comprise a firstfiber web (e.g., efficiency layer) having a relatively small andhomogeneous pore structure. In some embodiments, the maximum pore sizeof the first fiber web may be relatively small. For instance, in someembodiments, the first fiber web may have a maximum pore size of lessthan or equal to about 2.5 microns, less than or equal to about 2.3microns, less than or equal to about 2.0 microns, less than or equal toabout 1.8 microns, less than or equal to about 1.5 microns, less than orequal to about 1.4 microns, less than or equal to about 1.3 microns,less than or equal to about 1.2 microns, less than or equal to about 1.1microns, less than or equal to about 1.0 micron, less than or equal toabout 0.9 microns, less than or equal to about 0.8 microns, less than orequal to about 0.7 microns, less than or equal to about 0.6 microns,less than or equal to about 0.5 microns, less than or equal to about 0.4microns, less than or equal to about 0.3 microns, or less than or equalto about 0.2 microns. In some instances, the first fiber web may have amaximum pore size of greater than or equal to about 0.1 microns, greaterthan or equal to about 0.2 microns, greater than or equal to about 0.3microns, greater than or equal to about 0.4 microns, greater than orequal to about 0.5 microns, greater than or equal to about 0.6 microns,greater than or equal to about 0.7 microns, greater than or equal toabout 0.8 microns, greater than or equal to about 0.9 microns, greaterthan or equal to about 1.0 micron, greater than or equal to about 1.1microns, greater than or equal to about 1.2 microns, greater than orequal to about 1.4 microns, greater than or equal to about 1.6 microns,greater than or equal to about 1.8 microns, greater than or equal toabout 2.0 microns, or greater than or equal to about 2.2 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 0.1 microns and less than or equal toabout 2.5 microns, greater than or equal to about 0.5 microns and lessthan or equal to about 1.5 microns). Other values of maximum pore sizeare also possible. The maximum pore size may be determined via bubblepoint measurement according to the standard ASTM F-316-80 Method B,BS6410 (2011), e.g., using a Capillary Flow Porometer (e.g., modelnumber CFP-34RTF-8A-X6) made by Porous Materials Inc. and Galwick whichhas a fluid surface tension of 15.9 dynes/cm.

In some embodiments, the mean flow pore size of the first fiber web maybe less than or equal to about 1.0 micron, less than or equal to about0.9 microns, less than or equal to about 0.8 microns, less than or equalto about 0.7 microns, less than or equal to about 0.6 microns, less thanor equal to about 0.5 microns, less than or equal to about 0.4 microns,less than or equal to about 0.3 microns, less than or equal to about 0.1microns, or less than or equal to about 0.08 microns. In some instances,the mean flow pore size may be greater than or equal to about 0.05microns, greater than or equal to about 0.06 microns, greater than orequal to about 0.07 microns, greater than or equal to about 0.08microns, greater than or equal to about 0.1 microns, greater than orequal to about 0.2 microns, greater than or equal to about 0.3 microns,greater than or equal to about 0.4 microns, greater than or equal toabout 0.5 microns, greater than or equal to about 0.6 microns, greaterthan or equal to about 0.7 microns, greater than or equal to about 0.8microns, or greater than or equal to about 0.9 microns. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 0.05 microns and less than or equal to about 1 micron,greater than or equal to about 0.1 microns and less than or equal toabout 0.4 microns). The mean flow pore size may be determined accordingto the standard ASTM F-316-80 Method B, BS6410 (2011), e.g., using aCapillary Flow Porometer (e.g., model number CFP-34RTF-8A-X6) made byPorous Materials Inc. and Galwick, which has a fluid surface tension of15.9 dynes/cm.

In some embodiments, the pore characteristics of the first fiber web maybe relatively homogenous. For instance, in some embodiments, the ratioof maximum pore size to mean flow pore size of the first fiber web maybe less than or equal to about 5.0, less than or equal to about 4.8,less than or equal to about 4.5, less than or equal to about 4.2, lessthan or equal to about 4.0, less than or equal to about 3.8, less thanor equal to about 3.5, less than or equal to about 3.2, less than orequal to about 3.0, less than or equal to about 2.7, less than or equalto about 2.5, less than or equal to about 2.2, less than or equal toabout 2.0, less than or equal to about 1.8, less than or equal to about1.5, or less than or equal to about 1.2. In some instances, the ratio ofmaximum pore size to mean flow pore size may be greater than or equal toabout 1, greater than or equal to about 1.2, greater than or equal toabout 1.5, greater than or equal to about 1.8, greater than or equal toabout 2.0, greater than or equal to about 2.3, greater than or equal toabout 2.5, greater than or equal to about 2.8, greater than or equal toabout 3.0, greater than or equal to about 3.2, greater than or equal toabout 3.5, greater than or equal to about 3.8, greater than or equal toabout 4.0, greater than or equal to about 4.2, greater than or equal toabout 4.5, or greater than or equal to about 4.8. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1.0 and less than or equal to about 5.0, greater than or equalto about 2.3 and less than or equal to about 2.7). The ratio may bedetermined according to the standard ASTM F316-03 Method B, BS6410(2011) as described above.

As described in more detail below, the first fiber web may comprisesynthetic fibers (e.g., nylon fibers), amongst other fiber types. Insome instances, the first fiber web may comprise a relatively highweight percentage of synthetic fibers (e.g., greater than or equal toabout 95 wt. %, 100 wt. %). In some instances, the synthetic fibers maybe continuous as described further below. For example, the fiber web maycomprise a relatively high percentage (e.g., greater than or equal toabout 95 wt. %, 100 wt. %) of synthetic fibers formed via anelectrospinning process. In general, the first fiber web may comprisesynthetic fibers formed by any suitable process including anelectrospinning process, meltblown process, melt spinning process, orcentrifugal spinning process. In certain embodiments, the first fiberweb may comprise nylon and/or poly(ether sulfone) (PES) fibers. In someembodiments, an electrospinning process facilitates the formation of anefficiency layer with a small mean pore size and a narrow pore sizedistribution.

In some embodiments, the first fiber web may have an average fiberdiameter of less than or equal to about 0.5 microns, less than or equalto about 0.45 microns, less than or equal to about 0.4 microns, lessthan or equal to about 0.35 microns, less than or equal to about 0.3microns, less than or equal to about 0.25 microns, less than or equal toabout 0.2 microns, less than or equal to about 0.15 microns, less thanor equal to about 0.1 microns, less than or equal to about 0.09 microns,less than or equal to about 0.08 microns, less than or equal to about0.07 microns, or less than or equal to about 0.06 microns. In someinstances, the average fiber diameter of the first fiber web may begreater than or equal to about 0.05 microns, greater than or equal toabout 0.06 microns, greater than or equal to about 0.07 microns, greaterthan or equal to about 0.08 microns, greater than or equal to about 0.09microns, greater than or equal to about 0.1 microns, greater than orequal to about 0.15 microns, greater than or equal to about 0.2 microns,greater than or equal to about 0.25 microns, greater than or equal toabout 0.3 microns, greater than or equal to about 0.35 microns, greaterthan or equal to about 0.4 microns, or greater than or equal to about0.45 microns. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 0.05 microns and lessthan or equal to about 0.5 microns, greater than or equal to about 0.07microns and less than or equal to about 0.2 microns). Other values ofaverage fiber diameter are also possible.

In some embodiments, the first fiber web may be relatively thin. Forinstance, in some embodiments, the first fiber web may have a thicknessof less than or equal to about 200 microns, less than or equal to about175 microns, less than or equal to about 150 microns, less than or equalto about 125 microns, less than or equal to about 100) microns, lessthan or equal to about 75 microns, less than or equal to about 50microns, less than or equal to about 40 microns, less than or equal toabout 30 microns, less than or equal to about 20 microns, less than orequal to about 18 microns, less than or equal to about 15 microns, lessthan or equal to about 12 microns, less than or equal to about 10microns, or less than or equal to about 8 microns. In some instances,the first fiber web may have a thickness of greater than or equal toabout 5 microns, greater than or equal to about 6 microns, greater thanor equal to about 8 microns, greater than or equal to about 10 microns,greater than or equal to about 12 microns, greater than or equal toabout 15 microns, greater than or equal to about 18 microns, greaterthan or equal to about 20 microns, greater than or equal to about 25microns, greater than or equal to about 30 microns, greater than orequal to about 40 microns, greater than or equal to about 50 microns,greater than or equal to about 75 microns, greater than or equal toabout 100 microns, greater than or equal to about 125 microns, greaterthan or equal to about 150 microns, or greater than or equal to about175 microns. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 5 microns and less thanor equal to about 200 microns, greater than or equal to about 5 micronsand less than or equal to about 20 microns). Other values of averagethickness are also possible. In some embodiments, the thickness isdetermined using scanning electron microscopy (SEM). Thicknesses of 5micron or greater may be determined according to the standard ASTMD1777-96 (2015) using a pressure of 2.65 psi. Thicknesses less than 5micron may be determined using scanning electron microscopy.

In some embodiments, the first fiber web may have a relatively low basisweight. For instance, in some embodiments, the first fiber web may havea basis weight of less than or equal to about 10 g/m², less than orequal to about 9 g/m², less than or equal to about 8 g/m², less than orequal to about 7 g/m², less than or equal to about 6 g/m², less than orequal to about 5.0 g/m², less than or equal to about 4.5 g/m², less thanor equal to about 4.0 g/m², less than or equal to about 3.5 g/m², lessthan or equal to about 3.0 g/m², less than or equal to about 2.5 g/m²,less than or equal to about 2.0 g/m², less than or equal to about 1.5g/m², less than or equal to about 1.0 g/m², or less than or equal toabout 0.8 g/m². In some instances, the first fiber web may have a basisweight of greater than or equal to about 0.5 g/m², greater than or equalto about 1 g/m², greater than or equal to about 1.5 g/m², greater thanor equal to about 2.0 g/m², greater than or equal to about 2.5 g/m²,greater than or equal to about 3.0 g/m², greater than or equal to about3.5 g/m², greater than or equal to about 4.0 g/m², greater than or equalto about 5.0 g/m², greater than or equal to about 6 g/m², greater thanor equal to about 7 g/m², or greater than or equal to about 8 g/m².Combinations of the above-referenced ranges are possible (e.g., greaterthan or equal to about 0.5 g/m² and less than or equal to about 10 g/m²,greater than or equal to about 0.5 g/m² and less than or equal to about5.0 g/m², greater than or equal to about 1.0 g/m² and less than or equalto about 2.0 g/m²). Other values of basis weight are possible. The basisweight may be determined according to the standard ASTM D3776-09 (2009).

In certain embodiments, the first fiber web, described herein, may havea relatively low solidity. For instance, in some embodiments, the firstfiber web may have a solidity of less than or equal to about 30%, lessthan or equal to about 28%, less than or equal to about 25%, less thanor equal to about 22%, less than or equal to about 20%, less than orequal to about 18%, less than or equal to about 15%, less than or equalto about 12%, less than or equal to about 10%, less than or equal toabout 8%, or less than or equal to about 5%. In some instances, thefirst fiber web may have a solidity of greater than or equal to about2%, greater than or equal to about 5%, greater than or equal to about8%, greater than or equal to about 10%, greater than or equal to about12%, greater than or equal to about 15%, greater than or equal to about20%, greater than or equal to about 22%, greater than or equal to about25%, or greater than or equal to about 28%. It should be understood thatcombinations of the above-reference ranges are possible (e.g., greaterthan or equal to about 2% and less than or equal to about 30%, greaterthan or equal to about 5% and less than or equal to about 12%). Thesolidity is the volume percentage of a layer (e.g., fiber web) or afilter media occupied by solids (e.g., fibers) and is therefore the 100times ratio of the solids volume per unit mass divided by the volume perunit mass of the layer or media. The solidity, expressed as apercentage, can be derived from the fiber web porosity based on thefollowing equation: solidity (%)=100−porosity (%). Solidity, as usedherein, may also be determined by using the following formula: solidity(%)=[basis weight/(fiber density*thickness)]*100. The basis weight andthickness may be determined as described herein. In some embodiments,fiber density is equal to the density of the material (e.g., polymer) ofwhich the fiber(s) are made. For example, fiber density of polyamide 6fibers may be equal to the density of polyamide 6 (around 1.14 g/cc;cc=cm³).

In certain embodiments, the first fiber web, described herein, may havea relatively high surface area. For instance, in some embodiments, thefirst fiber web may have a surface area of greater than or equal toabout 5 m²/g, greater than or equal to about 10 m²/g, greater than orequal to about 25 m²/g, greater than or equal to about 50 m²/g, greaterthan or equal to about 75 m²/g, greater than or equal to about 100 m²/g,greater than or equal to about 125 m²/g, greater than or equal to about150 m²/g, greater than or equal to about 175 m²/g, greater than or equalto about 200 m²/g, greater than or equal to about 225 m²/g, greater thanor equal to about 250 m²/g, greater than or equal to about 275 m²/g, orgreater than or equal to about 300 m²/g. In some instances, the firstfiber web may have a surface area of less than or equal to about 350m²/g, less than or equal to about 325 m²/g, less than or equal to about300 m²/g, less than or equal to about 275 m²/g, less than or equal toabout 250 m²/g, less than or equal to about 225 m²/g, less than or equalto about 200 m²/g, less than or equal to about 175 m²/g, less than orequal to about 150 m²/g, less than or equal to about 125 m²/g, less thanor equal to about 100 m²/g, less than or equal to about 70 m²/g, lessthan or equal to about 40 m²/g, or less than or equal to about 10 m²/g.It should be understood that combinations of the above-referenced rangesare possible (e.g., greater than or equal to about 5 m²/g and less thanor equal to about 350 m²/g, greater than or equal to about 5 m²/g andless than or equal to about 70 m²/g, greater than or equal to about 5m²/g and less than or equal to about 75 m²/g).

As determined herein, surface area is measured through use of a standardBET surface area measurement technique. The BET surface area is measuredaccording to section 10 of Battery Council International StandardBCIS-03A, “Recommended Battery Materials Specifications Valve RegulatedRecombinant Batteries”, section 10 being “Standard Test Method forSurface Area of Recombinant Battery Separator Mat”. Following thistechnique, the BET surface area is measured via adsorption analysisusing a BET surface analyzer (e.g., Micromeritics Gemini III 2375Surface Area Analyzer) with nitrogen gas; the sample amount is between0.5 and 0.6 grams in, e.g., a ¾″ tube; and, the sample is allowed todegas at 75 degrees C. for a minimum of 3 hours.

As described herein, the filter media may comprise a second fiber web(e.g., calendered fiber web). In some embodiments, one or moreproperties of the second fiber web may impart beneficial properties tothe filter media, such as relatively homogeneous pore characteristicsand mechanical stability. For instance, certain pore characteristics(e.g., solidity, surface mean pore area, intersection density (number ofintersections per unit area), pore size), certain mechanical properties(e.g., tensile strength, tensile elongation), and/or the smoothness ofthe second fiber web may serve to promote relative pore homogeneityand/or provide mechanical stability for one or more fiber webs (e.g.,first fiber web). In some embodiments, a second fiber web with theabove-mentioned beneficial properties may be formed using a calenderingprocess. In some such cases, the second fiber web may be calenderedprior to combination with another fiber web (e.g., first fiber web) inthe filter media and/or inclusion into the filter media. In otherembodiments, a second fiber web with the above-mentioned beneficialproperties may be formed by casting a cross-linkable monomer solution(e.g., acrylate, acrylamide or cellulose monomers) on to anon-compressed fiber web (e.g., meltblown fiber web), such that thecross-linkable monomer solution fully wets the pores of thenon-compressed fiber web (e.g., meltblown fiber web). In some suchembodiments, crosslinking and polymerization of the monomer leads topore filling and strengthening of the fiber web. In some suchembodiments, crosslinking can be initiated via irradiation, or achemical process or a thermal treatment. The crosslinked or polymerizedmonomer may be a sacrificial layer that is removed after deposition ofthe first fiber web (e.g., efficiency layer).

In some embodiments, the distance between fibers in the second layer maybe relatively small. Without being bound by theory, it is believed thatfibers of the first fiber web are more likely to uniformly cover porousareas of the second fiber web (e.g., without defect and crack formation)when the distance between fibers in the second layer is small.

In some embodiments, the porosity of the second fiber web may be greaterthan or equal to about 35%, greater than or equal to about 40%, greaterthan or equal to about 45%, greater than or equal to about 50%, greaterthan or equal to about 55%, greater than or equal to about 60%, greaterthan or equal to about 65%, greater than or equal to about 70%, orgreater than or equal to about 75%. In some instances, the porosity ofthe second fiber web may less than or equal to about 80%, less than orequal to about 75%, less than or equal to about 70%, less than or equalto about 65%, less than or equal to about 60%, or less than or equal toabout 55%. It should be understood that combinations of theabove-referenced ranges are possible (e.g., greater than or equal toabout 50% and less than or equal to about 90%, greater than or equal toabout 70% and less than or equal to about 90%). In some embodiments, theporosity of the second fiber web is greater than or equal to about 35%and less than or equal to about 80%. The porosity of a fiber web,porosity (%)=100−solidity (%).

In certain embodiments, the second fiber web, described herein, may havea relatively small surface mean pore area. For instance, in someembodiments, the second fiber web may have a surface mean pore area ofless than or equal to about 50 μm², less than or equal to about 45 μm²,less than or equal to about 40 μm², less than or equal to about 35 μm²,less than or equal to about 30 μm², less than or equal to about 25 μm²,less than or equal to about 20 μm², less than or equal to about 15 μm²,less than or equal to about 10 μm², or less than or equal to about 5μm². In some instances, the second fiber web may have a surface meanpore area of greater than or equal to about 2 μm², greater than or equalto about 5 μm², greater than or equal to about 8 μm², greater than orequal about 10 μm², greater than or equal to about 15 μm², greater thanor equal to about 20 μm², greater than or equal to about 25 μm², greaterthan or equal to about 30 μm², greater than or equal to about 35 μm²,greater than or equal to about 40 μm², greater than or equal to about 45μm², or greater than or equal to about 50 μm². It should be understoodthat combinations of the above-reference ranges are possible (e.g.,greater than or equal to about 2 μm² and less than or equal to about 50μm², greater than or equal to about 5 μm² and less than or equal toabout 25 μm²). Other values of surface mean pore area of the secondfiber web are also possible.

As determined herein, the surface mean pore area is measured throughscanning electron microscopy analysis using DiameterJ, a plug-in for theImageJ image analysis software. A Phenom desktop scanning electronmicroscope can be used to generate the micrographs. The microscope maybe focused on a surface of a layer (e.g., a fiber web; e.g., a secondfiber web), e.g., at a zero degrees tilt. The micrographs can be takenat a magnification of 1200×. The electron acceleration voltage can be 10kV and backscattered electrons can be used to create the micrographs.The SEM micrographs (images) can be in gray scale. To measuregeometrical characteristics of an SEM image (e.g., average fiberdiameter, surface mean pore area, average fiber intersection density),ImageJ software can transform the SEM image from gray scale toblack-and-white image. In a black-and-white image, a black pixel canrepresent at least a portion of a pore (e.g., hole) and a white pixelcan represent at least a portion of a solid material (e.g., fiber). In acontinuous web such as a meltblown fiber web, collections of one or moreblack pixels, also referred to as black “islands,” may be surrounded bywhite pixels. A software algorithm in ImageJ can detect these black“islands”, count the number of black islands (the number of pores) andmeasure the area of each of them (the surface cross-sectional area ofeach pore, or pore area). The surface mean pore area can be calculatedby dividing the cumulative pore area of all pores in an SEM image by thenumber of pores in the image. Similarly, the software can count thenumber of white pixels and calculate fiber diameter, intersectiondensity, and/or other information.

In certain embodiments, the second fiber web, described herein, may havea relatively high number of fiber intersections per unit area. Forinstance, in some embodiments, the second fiber web may have greaterthan or equal to about 0.005 intersections/μm², greater than or equal toabout 0.006 intersections/μm², greater than or equal to about 0.007intersections/μm², greater than or equal to about 0.008intersections/μm², greater than or equal to about 0.009intersections/μm², greater than or equal to about 0.01intersections/μm², greater than or equal to about 0.012intersections/μm², greater than or equal to about 0.015intersections/m², greater than or equal to about 0.018intersections/μm², or greater than or equal to about 0.02intersections/μm². In some instances, the second fiber web may have lessthan or equal to about 0.025 intersections/μm², less than or equal toabout 0.022 intersections/μm², less than or equal to about 0.2intersections/μm², less than or equal to about 0.018 intersections/μm²,less than or equal to about 0.015 intersections/μm², less than or equalto about 0.012 intersections/μm², less than or equal to about 0.01intersections/μm², less than or equal to about 0.009 intersections/μm²,less than or equal to about 0.008 intersections/μm², less than or equalto about 0.007 intersections/μm², or less than or equal to about 0.006intersections/μm². It should be understood that combinations of theabove-reference ranges are possible (e.g., greater than or equal toabout 0.005 intersections/μm² and less than or equal to about 0.025intersections/μm², greater than or equal to about 0.008intersections/μm² and less than or equal to about 0.02intersections/μm²).

As determined herein, the number of fiber intersections per micronsquared may be measured through scanning electron microscopy analysisusing ImageJ image analysis software. A Phenom desktop scanning electronmicroscope can be used to generate the micrographs. The microscope maybe focused on a surface of a layer (e.g., a fiber web, e.g., a secondfiber web), e.g., at a zero degrees tilt. The micrographs can be takenat a magnification of 1200×. The electron acceleration voltage can be 10kV and backscattered electrons can be used to create the micrographs.The total number of intersections between fibers at the surface of thelayer can be determined by counting the intersections in a micrographand dividing the number of intersections by the area covered by themicrograph.

In some embodiments, the second fiber web may have a maximum pore sizeof less than or equal to about 80 microns, less than or equal to about70 microns, less than or equal to about 60 microns, less than or equalto about 50 microns, less than or equal to about 40 microns, less thanor equal to about 30 microns, less than or equal to about 20 microns, orless than or equal to about 15 microns. In some instances, the secondfiber web may have a maximum pore size of greater than or equal to about10 microns, greater than or equal to about 20 microns, greater than orequal to about 30 microns, greater than or equal to about 40 microns,greater than or equal to about 50 microns, greater than or equal toabout 60 microns, or greater than or equal to about 70 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 10 microns and less than or equal toabout 80 microns, greater than or equal to about 30 microns and lessthan or equal to about 80 microns, greater than or equal to about 70microns and less than or equal to about 80 microns). Other values ofmaximum pore size are also possible.

In some embodiments, the mean flow pore size of the second fiber web(e.g., calendered fiber web) may be less than or equal to about 30microns, less than or equal to about 28 microns, less than or equal toabout 25 microns, less than or equal to about 22 microns, less than orequal to about 20 microns, less than or equal to about 18 microns, lessthan or equal to about 15 microns, less than or equal to about 12microns, less than or equal to about 10 microns, less than or equal toabout 8 microns, less than or equal to about 5 microns, less than orequal to about 4 microns, or less than or equal to about 2 microns. Insome instances, the mean flow pore size may be greater than or equal toabout 1 micron, greater than or equal to about 2 microns, greater thanor equal to about 5 microns, greater than or equal to about 8 microns,greater than or equal to about 10 microns, greater than or equal toabout 12 microns, greater than or equal to about 15 microns, greaterthan or equal to about 20 microns, greater than or equal to about 22microns, greater than or equal to about 25 microns, or greater than orequal to about 28 microns. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 1 micron andless than or equal to about 30 microns, greater than or equal to about10 microns and less than or equal to about 20 microns).

As noted above, in some embodiments, the second fiber web may berelatively resistant to deformation without being brittle. For instance,the second fiber web may have a relatively high tensile strength and/ora tensile elongation. Without being bound by theory, it is believed thatthe resistance to deformation may significantly reduce the likelihood ofdamage to the first fiber web that could be induced by some physicalstress. This type of stress may originate, e.g., from web handling (e.g.unwinding/rewinding, laminating, collating and slitting steps),pleating, and the cartridge assembly phase. If the second fiber webundergoes significant deformation when the product is fabricated, thestability and properties of the first fiber web may be affected.

In some embodiments, the second fiber web (e.g., calendered fiber web)may have a dry tensile strength in the machine direction of greater thanor equal to about 1 lb/in, greater than or equal to about 2 lb/in,greater than or equal to about 5 lb/in, greater than or equal to about 8lb/in, greater than or equal to about 10 lb/in, greater than or equal toabout 12 lb/in, greater than or equal to about 15 lb/in, greater than orequal to about 18 lb/in, greater than or equal to about 20 lb/in,greater than or equal to about 22 lb/in, greater than or equal to about25 lb/in, or greater than or equal to about 30 lb/in. In some instances,the dry tensile strength in the machine direction may be less than orequal to about 35 lb/in, less than or equal to about 32 lb/in, less thanor equal to about 30 lb/n, less than or equal to about 28 lb/in, lessthan or equal to about 25 lb/in, less than or equal to about 20 lb/in,less than or equal to about 15 lb/in, less than or equal to about 10lb/in, or less than or equal to about 5 lb/in. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1 lb/in and less than or equal to about 35 lb/in, greater thanor equal to about 2 lb/in and less than or equal to about 30 lb/in).Other values of dry tensile strength in the machine direction are alsopossible. The dry tensile strength in the machine direction may bedetermined according to the standard ASTM D5035-11 (2015).

In some embodiments, the second fiber web (e.g., calendered fiber web)may have a dry tensile strength in the cross direction of greater thanor equal to about 1 lb/in, greater than or equal to about 2 lb/in,greater than or equal to about 5 lb/in, greater than or equal to about 8lb/in, greater than or equal to about 10 lb/in, greater than or equal toabout 12 lb/in, greater than or equal to about 15 lb/in, greater than orequal to about 18 lb/in, greater than or equal to about 20 lb/in,greater than or equal to about 22 lb/in, greater than or equal to about25 lb/in, or greater than or equal to about 30 lb/in. In some instances,the dry tensile strength in the cross direction may be less than orequal to about 35 lb/in, less than or equal to about 32 lb/in, less thanor equal to about 30 lb/in, less than or equal to about 28 lb/in, lessthan or equal to about 25 lb/in, less than or equal to about 20 lb/in,less than or equal to about 15 lb/in, less than or equal to about 10lb/in, or less than or equal to about 5 lb/in. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1 lb/in and less than or equal to about 35 lb/in, greater thanor equal to about 2 lb/in and less than or equal to about 30 lb/in).Other values of dry tensile strength in the cross direction are alsopossible. The dry tensile strength in the cross direction may bedetermined according to the standard ASTM D5035-11 (2015).

In some embodiments, the second fiber web (e.g., calendered fiber web)may have a dry tensile elongation in the machine direction of greaterthan or equal to about 10%, greater than or equal to about 13%, greaterthan or equal to about 15%, greater than or equal to about 20%, greaterthan or equal to about 25%, greater than or equal to about 30%, greaterthan or equal to about 350/%, greater than or equal to about 40%,greater than or equal to about 45%, greater than or equal to about 50%,or greater than or equal to about 55%. In some instances, the drytensile elongation in the machine direction may be less than or equal toabout 60%, less than or equal to about 55%, less than or equal to about50%, less than or equal to about 45%, less than or equal to about 40%,less than or equal to about 35%, less than or equal to about 30%, lessthan or equal to about 25%, less than or equal to about 20%, or lessthan or equal to about 15%. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 10% and lessthan or equal to about 60%, greater than or equal to about 13% and lessthan or equal to 50%). Other values of dry tensile elongation in themachine direction are also possible. The dry tensile elongation in themachine direction may be determined according to the standard ASTMD5035-11 (2015).

In some embodiments, the second fiber web (e.g., calendered fiber web)may have a dry tensile elongation in the cross direction of greater thanor equal to about 5%, greater than or equal to about 10%, greater thanor equal to about 13%, greater than or equal to about 15%, greater thanor equal to about 20%, greater than or equal to about 25%, greater thanor equal to about 30%, greater than or equal to about 35%, greater thanor equal to about 40%, greater than or equal to about 45%, greater thanor equal to about 50%, or greater than or equal to about 55%. In someinstances, the dry tensile elongation in the cross direction may be lessthan or equal to about 70%, less than or equal to about 65%, less thanor equal to about 60%, less than or equal to about 55%, less than orequal to about 50%, less than or equal to about 45%, less than or equalto about 40%, less than or equal to about 35%, less than or equal toabout 30%, less than or equal to about 25%, less than or equal to about20%, or less than or equal to about 15%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 5% and less than or equal to about 70%, greater than or equalto about 10% and less than or equal to about 60%, greater than or equalto about 13% and less than or equal to 50%/o). Other values of drytensile elongation in the cross direction are also possible. The drytensile elongation in the cross direction may be determined according tothe standard ASTM D5035-11 (2015).

In some embodiments, at least a portion of a surface of the second fiberweb is to relatively smooth. Without being bound by theory, it isbelieved that: (i) smooth surfaces can provide a high degree (e.g.,areal density) of contact points between the efficiency layer (e.g.,fiber web having an average fiber diameter of less than or equal toabout 0.5 microns) and the surface of the support layer, which mayreduce the amount of localized stress on the efficiency layer under anexternal source of pressure; and (ii) smooth surfaces have a relativelysmall surface roughness, which may reduce the amount of curvature of thenanofiber layer when conforming to the smooth surface, which may reducethe amount of internal stresses in the nanofiber layer. In someinstances, smoothness may be imparted to a surface of the second fiberweb by one or more manufacturing and/or processing steps. For instance,in some embodiments, the second fiber web (e.g., support layer) is acalendered fiber web. Without being bound by theory, it is believed thatthe calendering process may decrease or eliminate the amount of loosefiber ends on the surface of the second fiber web, which might protrudeinto or through the efficiency layer and cause defects in the efficiencylayer. In certain embodiments, fibers with different diameters (e.g.,staple fibers, continuous fibers) may be mixed or used to enhance ordecrease surface roughness. Non-limiting examples of methods forimparting smoothness to a surface of the second fiber web includecalendering, chemical and/or bio-polishing, flame singeing, and surfacecoating.

In some embodiments, the root mean square of surface roughness of thesecond fiber web may be less than or equal to about 50 microns, lessthan or equal to about 40 microns, less than or equal to about 30microns, less than or equal to about 20 microns, less than or equal toabout 15 microns, less than or equal to about 12 microns, less than orequal to about 10 microns, less than or equal to about 8 microns, lessthan or equal to about 5 microns, or less than or equal to about 2microns. In some instances, the root mean square of surface roughness ofthe second fiber web may be greater than or equal to about 1 micron,greater than or equal to about 2 microns, greater than or equal to about3 microns, greater than or equal to about 4 microns, greater than orequal to about 5 microns, greater than or equal to about 6 microns,greater than or equal to about 8 microns, greater than or equal to about10 microns, greater than or equal to about 15 microns, greater than orequal to about 20 microns, greater than or equal to about 30 microns, orgreater than or equal to about 40 microns. Combinations of the abovereferenced ranges are also possible (e.g., greater than or equal toabout 1 micron and less than or equal to about 50 microns, greater thanor equal to about 3 microns and less than or equal to about 10 microns).The root mean square roughness of surface roughness may be determinedusing confocal laser microscopy. This test was performed following ISO25178-1 (2016) standard.

In some embodiments, the second fiber web may be relatively lightweight.For instance, in some embodiments, the second fiber web may have a basisweight of less than or equal to about 50 g/m², less than or equal toabout 45 g/m², less than or equal to about 40 g/m², less than or equalto about 35 g/m², less than or equal to about 30 g/m², less than orequal to about 25 g/m², less than or equal to about 20 g/m², or lessthan or equal to about 15 g/m². In some instances, the second fiber webmay have a basis weight of greater than or equal to about 10 g/m²,greater than or equal to about 15 g/m², greater than or equal to about20 g/m², greater than or equal to about 25 g/m², greater than or equalto about 30 g/m², greater than or equal to about 35 g/m², greater thanor equal to about 40 g/m², or greater than or equal to about 45 g/m².Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 10 g/m² and less than or equal to about50 g/m², greater than or equal to about 20 g/m² and less than or equalto about 35 g/m²). Other values of basis weight are also possible.

In some embodiments, the second fiber web may be relatively thin. Forinstance, in some embodiments, the second fiber web may have a thicknessof less than or equal to about 400 microns, less than or equal to about350 microns, less than or equal to about 300 microns, less than or equalto about 250 microns, less than or equal to about 200 microns, less thanor equal to about 180 microns, less than or equal to about 150 microns,less than or equal to about 120 microns, less than or equal to about 100microns, less than or equal to about 80 microns, or less than or equalto about 50 microns. In some instances, the second fiber web may have athickness of greater than or equal to about 25 microns, greater than orequal to about 30 microns, greater than or equal to about 50 microns,greater than or equal to about 80 microns, greater than or equal toabout 100 microns, greater than or equal to about 120 microns, greaterthan or equal to about 150 microns, greater than or equal to about 180microns, greater than or equal to about 200 microns, greater than orequal to about 220 microns, greater than or equal to about 250 microns,greater than or equal to about 280 microns, greater than or equal toabout 300 microns, greater than or equal to about 320 microns, orgreater than or equal to about 350 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 25 microns and less than or equal to about 400 microns, greaterthan or equal to about 50 microns and less than or equal to about 180microns). Other values of average thickness are also possible. In someembodiments, the thickness of the second fiber web may be determinedaccording to ASTM D1777-96 (2015) using a pressure of 2.65 psi.

As described in more detail below, the second fiber web may comprisesynthetic fibers, amongst other fiber types. In some instances, thesecond fiber web may comprise a relatively high weight percentage ofsynthetic fibers (e.g., greater than or equal to about 95 wt. %, 100 wt.%). In some instances, the synthetic fibers (e.g., nylon fibers,propylene fibers) may be continuous as described further below. Forexample, the second fiber web may comprise a relatively high percentage(e.g., greater than or equal to about 95 wt. %, 100 wt. %) of syntheticfibers formed via a meltblowing process. In general, the second fiberweb may comprise synthetic fibers formed by any suitable processincluding a meltblown process, melt spinning process, centrifugalspinning process, non-wet laid process, and/or wetlaid process.

In some embodiments, the second fiber web may have an average fiberdiameter of less than or equal to about 50 microns, less than or equalto about 45 microns, less than or equal to about 40 microns, less thanor equal to about 35 microns, less than or equal to about 30 microns,less than or equal to about 25 microns, less than or equal to about 20microns, less than or equal to about 15 microns, less than or equal toabout 10 micron, or less than or equal to about 5 microns. In someinstances, the average fiber diameter may be greater than or equal toabout 2 microns, greater than or equal to about 5 microns, greater thanor equal to about 10 micron, greater than or equal to about 15 microns,greater than or equal to about 20 micron, greater than or equal to about25 microns, greater than or equal to about 30 microns, greater than orequal to about 35 microns, greater than or equal to about 40 microns, orgreater than or equal to about 45 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 2 microns and less than or equal to about 50 microns, greaterthan or equal to about 2 microns and less than or equal to about 30microns). Other values of average fiber diameter are also possible.

As noted above, the filter media may include a third fiber web bonded(e.g., adhesively bonded, via lamination) to the first fiber web. Thethird fiber web may impart beneficial properties to the filter media.For instance, the third fiber web may be a non-filtration layer thatserves to protect the first fiber web from potential mechanical damagesduring processing and handling. In some embodiments, the third fiber webis configured to act as a pre-filtration layer that increases the dirtholding capacity of the filter media. In certain embodiments, the thirdfiber web is configured to act as both a pre-filtration layer and aprotective layer. In certain embodiments, the third fiber web may impartbeneficial particulate capture properties to the filter media. Forexample, the third fiber web may be an efficiency layer. In some suchcases, the third fiber web may have one or more properties substantiallysimilar to and/or the same as the first fiber web. Regardless of thefunction of the third fiber web, the third fiber web may be bonded(e.g., via lamination, adhesively) to the first fiber web.

In some embodiments (e.g., in which the third fiber web is anon-filtration layer), the third layer may have relatively large pores.For instance, in some embodiments, the third fiber web may have amaximum pore size of greater than or equal to about 20 microns, greaterthan or equal to about 25 microns, greater than or equal to about 30microns, greater than or equal to about 35 microns, greater than orequal to about 40 microns, greater than or equal to about 45 microns,greater than or equal to about 50 microns, or greater than or equal toabout 55 microns. In some instances, the third fiber web may have amaximum pore size of less than or equal to about 70 microns, less thanor equal to about 60 microns, less than or equal to about 56 microns,less than or equal to about 50 microns, less than or equal to about 45microns, less than or equal to about 40 microns, less than or equal toabout 35 microns, less than or equal to about 30 microns, or less thanor equal to about 25 microns. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 20microns and less than or equal to about 70 micron, greater than or equalto about 20 microns and less than or equal to about 60 micron, greaterthan or equal to about 30 microns and less than or equal to about 56microns). Other values of maximum pore size are also possible.

In some embodiments (e.g., in which the third fiber web is anon-filtration layer), the mean flow pore size of the third fiber webmay be greater than or equal to about 5 micron, greater than or equal toabout 8 microns, greater than or equal to about 10 microns, greater thanor equal to about 12 microns, greater than or equal to about 15 microns,greater than or equal to about 18 microns, greater than or equal toabout 20 microns, greater than or equal to about 22 microns, greaterthan or equal to about 25 microns, or greater than or equal to about 28microns. In some instances, the mean flow pore size may be less than orequal to about 30 microns, less than or equal to about 28 microns, lessthan or equal to about 25 microns, less than or equal to about 22microns, less than or equal to about 20 microns, less than or equal toabout 18 microns, less than or equal to about 15 microns, less than orequal to about 12 microns, less than or equal to about 10 microns, orless than or equal to about 8 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 5 micron and less than or equal to about 30 microns, greaterthan or equal to about 15 microns and less than or equal to about 25microns). It should be understood that in some embodiments (e.g., inwhich the third fiber web is a filtration layer), the maximum pore sizeand/or the mean flow pore size may be substantially similar to and/orthe same as one or more fiber webs described herein (e.g., first fiberweb, second fiber web, fourth fiber web).

In some embodiments, the third fiber web may have a basis weight of lessthan or equal to about 30 g/m², less than or equal to about 28 g/m²,less than or equal to about 25 g/m², less than or equal to about 22g/m², less than or equal to about 20 g/m², less than or equal to about18 g/m², less than or equal to about 15 g/m², less than or equal toabout 12 g/m², less than or equal to about 10 g/m², or less than orequal to about 8 g/m². In some instances, the third fiber web may have abasis weight of greater than or equal to about 5 g/m², greater than orequal to about 8 g/m², greater than or equal to about 10 g/m², greaterthan or equal to about 12 g/m², greater than or equal to about 15 g/m²,greater than or equal to about 18 g/m², greater than or equal to about20 g/m², greater than or equal to about 22 g/m², greater than or equalto about 25 g/m², or greater than or equal to about 28 g/m².Combinations of the above-referenced ranges are possible (e.g., greaterthan or equal to about 5 g/m² and less than or equal to about 30 g/m²,greater than or equal to about 10 g/m² and less than or equal to about25 g/m²). Other values of basis weight are possible. The basis weightmay be determined according to the standard ASTM D3776 (2017). It shouldbe understood that in some embodiments (e.g., in which the third fiberweb is a filtration layer), the basis weight may be substantiallysimilar to and/or the same as one or more fiber webs described herein(e.g., first fiber web, second fiber web, fourth fiber web).

In some embodiments, the third fiber web may be relatively thin. Forinstance, in some embodiments, the third fiber web may have a thicknessof less than or equal to about 250 microns, less than or equal to about225 microns, less than or equal to about 200 microns, less than or equalto about 175 microns, less than or equal to about 150 microns, less thanor equal to about 125 microns, or less than or equal to about 100microns. In some instances, the third fiber web may have a thickness ofgreater than or equal to about 80 microns, greater than or equal toabout 100 microns, greater than or equal to about 125 microns, greaterthan or equal to about 150 microns, greater than or equal to about 175microns, greater than or equal to about 200 microns, or greater than orequal to about 225 microns. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 80 microns andless than or equal to about 250 microns, greater than or equal to about100 microns and less than or equal to about 150 microns). Other valuesof average thickness are also possible. In some embodiments, thethickness may be determined according to the standard ASTM D1777-96(2015) using a pressure of 2.65 psi. It should be understood that insome embodiments (e.g., in which the third fiber web is a filtrationlayer), the thickness may be substantially similar to and/or the same asone or more fiber webs described herein (e.g., first fiber web, secondfiber web, fourth fiber web).

As described in more detail below, the third fiber web may comprisesynthetic fibers, amongst other fiber types. In some instances, thethird fiber web may comprise a relatively high weight percentage ofsynthetic fibers (e.g., greater than or equal to about 95 wt. %, 100 wt.%). In some instances, the synthetic fibers may be continuous asdescribed further below. For example, the third fiber web may comprise arelatively high percentage (e.g., greater than or equal to about 95 wt.%, 100 wt. %) of synthetic fibers formed via a meltblowing process. Ingeneral, the third fiber web may comprise synthetic fibers formed by anysuitable process including a meltblown process, melt spinning process,centrifugal spinning process, non-wet laid process, and/or wetlaidprocess.

In some embodiments, the average fiber diameter of the third fiber webmay be greater than or equal to about 1 micron, greater than or equal toabout 2 microns, greater than or equal to about 3 microns, greater thanor equal to about 4 microns, greater than or equal to about 5 microns,greater than or equal to about 8 microns, greater than or equal to about10 microns, greater than or equal to about 12 microns, greater than orequal to about 15 microns, or greater than or equal to about 18 microns.In some instances, the third fiber web may have an average fiberdiameter of less than or equal to about 20 microns, less than or equalto about 18 microns, less than or equal to about 15 microns, less thanor equal to about 12 microns, less than or equal to about 10 microns,less than or equal to about 8 microns, less than or equal to about 6microns, less than or equal to about 5 microns, less than or equal toabout 4 microns, or less than or equal to about 3 microns. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to about 1 micron and less than or equal to about 20 microns,greater than or equal to about 2 microns and less than or equal to about15 microns). Other values of average fiber diameter are also possible.It should be understood that in some embodiments (e.g., in which thethird fiber web is a filtration layer), the average fiber diameter maybe substantially similar to and/or the same as one or more fiber websdescribed herein (e.g., first fiber web, second fiber web, fourth fiberweb).

In some embodiments, one or more additional fiber webs or components areincluded with the filter media. In certain embodiments, the filter mediamay include one or more additional fiber webs. For instance, the filtermedia may include four or more (e.g., five or more, six or more, sevenor more) fiber webs. In some embodiments, the additional fiber web maybe a protective layer. For instance, the filter media may comprise afirst fiber web (e.g., efficiency layer) adjacent to (e.g., directlyadjacent to) a second fiber web (e.g., calendered fiber web) and a thirdfiber web (e.g., efficiency layer) and a fourth fiber web (e.g.,protective fiber web) adjacent to (e.g., directly adjacent to) to thethird fiber web. In such cases, the filter media may also comprise afifth fiber web (e.g., support layer) adjacent to (e.g., directlyadjacent to) the second fiber web. In some embodiments, the additionalfiber web may be a support layer. In some such cases, the support layer(e.g., spunbond fiber web) may be adjacent to the second fiber web. Asanother example, the filter media may comprise a first fiber web (e.g.,efficiency layer) adjacent to (e.g., directly adjacent to) a secondfiber web (e.g., calendered fiber web) and a third fiber web (e.g.,protective layer) and a fourth fiber web (e.g., support layer) adjacentto (e.g., directly adjacent to) to the second fiber web.

Non-limiting examples of additional fiber webs (e.g., a fourth fiberweb, fifth fiber web) include a meltblown fiber web, a wet laid fiberweb, a spunbond fiber web, a carded fiber web, an air-laid fiber web, aspunlace fiber web, a forcespun fiber web or an electrospun fiber web.

As noted above, filter media described herein may have a relativelysmall and homogeneous pore structure. In some embodiments, the filtermedia may have a relatively small mean flow and/or maximum pore size.For instance, in some embodiments, the filter media has a mean flow poresize of less than or equal to about 1.0 micron, less than or equal toabout 0.9 microns, less than or equal to about 0.8 microns, less than orequal to about 0.7 microns, less than or equal to about 0.6 microns,less than or equal to about 0.5 microns, less than or equal to about 0.4microns, less than or equal to about 0.3 microns, less than or equal toabout 0.1 microns, or less than or equal to about 0.08 microns. In someinstances, the mean flow pore size may be greater than or equal to about0.05 microns, greater than or equal to about 0.06 microns, greater thanor equal to about 0.07 microns, greater than or equal to about 0.08microns, greater than or equal to about 0.1 microns, greater than orequal to about 0.2 microns, greater than or equal to about 0.3 microns,greater than or equal to about 0.4 microns, greater than or equal toabout 0.5 microns, greater than or equal to about 0.6 microns, greaterthan or equal to about 0.7 microns, greater than or equal to about 0.8microns, or greater than or equal to about 0.9 microns. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 0.05 microns and less than or equal to about 1 micron,greater than or equal to about 0.1 microns and less than or equal toabout 0.4 microns).

In some embodiments, the filter media has a maximum pore size of lessthan or equal to about 2.5 microns, less than or equal to about 2.3microns, less than or equal to about 2.0 microns, less than or equal toabout 1.8 microns, less than or equal to about 1.6 microns, less than orequal to about 1.4 microns, less than or equal to about 1.3 microns,less than or equal to about 1.2 microns, less than or equal to about 1.1microns, less than or equal to about 1.0 micron, less than or equal toabout 0.9 microns, less than or equal to about 0.8 microns, less than orequal to about 0.7 microns, less than or equal to about 0.6 microns,less than or equal to about 0.5 microns, less than or equal to about 0.4microns, less than or equal to about 0.3 microns, or less than or equalto about 0.2 microns. In some instances, the first fiber web may have amaximum pore size of greater than or equal to about 0.1 microns, greaterthan or equal to about 0.2 microns, greater than or equal to about 0.3microns, greater than or equal to about 0.4 microns, greater than orequal to about 0.5 microns, greater than or equal to about 0.6 microns,greater than or equal to about 0.7 microns, greater than or equal toabout 0.8 microns, greater than or equal to about 0.9 microns, greaterthan or equal to about 1.0 micron, greater than or equal to about 1.1microns, greater than or equal to about 1.2 microns, greater than orequal to about 1.4 microns, greater than or equal to about 1.6 microns,greater than or to equal to about 1.8 microns, greater than or equal toabout 2.0 microns, or greater than or equal to about 2.2 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 0.1 microns and less than or equal toabout 2.5 microns, greater than or equal to about 0.5 microns and lessthan or equal to about 1.3 microns).

In some embodiments, the ratio of maximum pore size to mean flow poresize of the filter media may be less than or equal to about 5.0, lessthan or equal to about 4.8, less than or equal to about 4.5, less thanor equal to about 4.2, less than or equal to about 4.0, less than orequal to about 3.8, less than or equal to about 3.5, less than or equalto about 3.2, less than or equal to about 3.0, less than or equal toabout 2.7, less than or equal to about 2.5, less than or equal to about2.2, less than or equal to about 2.0, less than or equal to about 1.8,less than or equal to about 1.5, or less than or equal to about 1.2. Insome instances, the ratio of maximum pore size to mean flow pore sizemay be greater than or equal to about 1, greater than or equal to about1.2, greater than or equal to about 1.5, greater than or equal to about1.8, greater than or equal to about 2.0, greater than or equal to about2.3, greater than or equal to about 2.5, greater than or equal to about2.8, greater than or equal to about 3.0, greater than or equal to about3.2, greater than or equal to about 3.5, greater than or equal to about3.8, greater than or equal to about 4.0, greater than or equal to about4.2, greater than or equal to about 4.5, or greater than or equal toabout 4.8. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 1.0 and less than or equal toabout 5.0, greater than or equal to about 2.3 and less than or equal toabout 2.7).

In some embodiments, the full width at half maximum of the poredistribution of the filter media is less than or equal to about 0.2microns, less than or equal to about 0.18 microns, less than or equal toabout 0.15 microns, less than or equal to about 0.12 microns, less thanor equal to about 0.1 microns, less than or equal to about 0.08 microns,less than or equal to about 0.05 microns, less than or equal to about0.02 microns, less than or equal to about 0.01 microns, less than orequal to about 0.008 microns, less than or equal to about 0.005 microns,or less than or equal to about 0.002 microns. In some instances, thefull width at half maximum of the pore distribution of the filter mediais greater than or equal to about 0.001 microns, greater than or equalto about 0.002 microns, greater than or equal to about 0.004 microns,greater than or equal to about 0.006, greater than or equal to about0.008 microns, greater than or equal to to about 0.01 microns, greaterthan or equal to about 0.02 microns, greater than or equal to about 0.05microns, greater than or equal to about 0.08 microns, greater than orequal to about 0.1 microns, greater than or equal to about 0.12 microns,or greater than or equal to about 0.15 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0.001 microns and less than or equal to about 0.2 microns,greater than or equal to about 0.004 microns and less than or equal toabout 0.1 microns). The full width at half maximum (FWHM) may bedetermined according to the standard ASTM F316-03 (2011). Briefly. FWHMmay be calculated from fitting a histogram of pore size using alog-normal distribution model. The FWHM may then be calculated based oncharacteristic values of the model. For example, one of skill in the artmay derive the following expression for calculating FWHM for alog-normal distribution:

FWHM=EXP(Scale*SQRT(−4*Location+2*(Scale{circumflex over( )}2)−1.38629)+Location−Scale{circumflex over( )}2)−EXP(−Scale*SQRT(−4*Location+2*(Scale{circumflex over( )}2)−1.38629)+Location-Scale{circumflex over ( )}2). In suchembodiments, Scale and Location parameters are outcomes of thestatistical model.

In some embodiments, the filter media may have a relatively uniform meanflow pore size. For example, the standard deviation in maximum pore sizewhen measured across the fibrous layer may be relatively small. Forinstance, in some embodiments, the standard deviation in maximum poresize when measured across the filter media may be less than or equal toabout 2 microns, less than or equal to about 1.8 microns, less than orequal to about 1.6 microns, less than or equal to about 1.4 microns,less than or equal to about 1.2 microns, less than or equal to about 1micron, less than or equal to about 0.8 microns, less than or equal toabout 0.6 microns, less than or equal to about 0.4 microns, less than orequal to about 0.2 microns, or less than or equal to about 0.1 microns.In some instances, the standard deviation in maximum pore size may begreater than or equal to about 0 microns, greater than or equal to about0.2 micron, greater than or equal to about 0.4 microns, greater than orequal to about 0.6 microns, greater than or equal to about 0.8 microns,greater than or equal to about 1 micron, greater than or equal to 1.2about microns, greater than or equal to about 1.4 microns, greater thanor equal to about 1.6 microns, or greater than or equal to about 1.8microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to about 0 microns and less than or equalto about 2 microns, greater than or equal to about 0 micron and lessthan or equal to about 1 micron). The standard deviation in maximum poresize may be determined according to the standard ASTM F316-03 (2011).Briefly, the maximum pore size may be taken at regularly spacedintervals (e.g., 7 inches apart) along the width of the material. Thestandard deviation can be determined from a statistically significantnumber of samples (e.g., from at least eight (8) measurements per filtermedia, e.g., from 12 measurements per filter media). For example, todetermine the standard deviation of a filter media having an area of 1m², a width of 2 m, and a length of 0.5 m, the mean flow pore size canbe measured at 12 locations along the width of the filter media. Thefirst measurement can be taken 4 inches from an edge of the filter mediathat is used to determine the width and the last measurement can betaken 4 inches from the other edge used to determine the width. Theremaining measurements can be spaced across the width, such that the 12measurements are approximately equidistant apart. The standard deviationcan be calculated using methods known to those of ordinary skill in theart.

In some embodiments, the water bubble point of the filter media and/or afiber web (e.g., first fiber web) may be greater than or equal to about30 psi, greater than or equal to about 40 psi, greater than or equal toabout 50 psi, greater than or equal to about 60 psi, greater than orequal to about 65 psi, greater than or equal to about 70 psi, greaterthan or equal to about 75 psi, greater than or equal to about 80 psi,greater than or equal to about 85 psi, greater than or equal to about 90psi, or greater than or equal to about 95 psi. In some instances, thewater bubble point may be less than or equal to about 120 psi, less thanor equal to about 110 psi, less than or equal to about 100 psi, lessthan or equal to about 95 psi, less than or equal to about 90 psi, lessthan or equal to about 85 psi, less than or equal to about 80 psi, lessthan or equal to about 75 psi, less than or equal to about 70 psi, orless than or equal to about 60 psi. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 30 psiand less than or equal to about 120 psi, greater than or equal to about60 psi and less than or equal to about 100 psi, greater than or equal toabout 60 psi and less than or equal to about 90 psi). Other values ofwater bubble point are also possible. The water bubble point may bedetermined according to according to the standard ASTM F-316-80 MethodB, BS6410 (2011).

In some embodiments, the filter media may be relatively thin. Forinstance, in some embodiments, the thickness of the filter media may beless than or equal to about 400 microns, less than or equal to about 375microns, less than or equal to about 350 microns, less than or equal toabout 325 microns, less than or equal to about 300 microns, less than orequal to about 275 microns, less than or equal to about 250 microns,less than or equal to about 225 microns, less than or equal to about 200microns, less than or equal to about 175 microns, less than or equal toabout 150 microns, or less than or equal to about 125 microns. In someinstances, the thickness may be greater than or equal to about 100microns, greater than or equal to about 130 microns, greater than orequal to about 150 microns, greater than or equal to about 175 microns,greater than or equal to about 200 microns, greater than or equal toabout 225 microns, greater than or equal to about 250 microns, greaterthan or equal to about 275 microns, greater than or equal to about 300microns, greater than or equal to about 325 microns, or greater than orequal to about 350 microns. Combinations of the above referenced rangesare also possible (e.g., greater than or equal to about 100 microns andless than or equal to about 400 microns, greater than or equal to about130 microns and less than or equal to about 300 microns). In someembodiments, the thickness may be determined according to the standardASTM D1777-96 (2015) at 2.6 psi.

In some embodiments, the filter media may be relatively lightweight. Forinstance, in some embodiments, the filter media may have a basis weightof less than or equal to about 80 g/m², less than or equal to about 75g/m², less than or equal to about 70 g/m², less than or equal to about65 g/m², less than or equal to about 62 g/m², less than or equal toabout 60 g/m², less than or equal to about 58 g/m², less than or equalto about 55 g/m², less than or equal to about 52 g/m², less than orequal to about 50 g/m², less than or equal to about 48 g/m², or lessthan or equal to about 45 g/m². In some instances, the filter media mayhave a basis weight of greater than or equal to about 40 g/m², greaterthan or equal to about 42 g/m², greater than or equal to about 45 g/m²,greater than or equal to about 48 g/m², greater than or equal to about50 g/m², greater than or equal to about 55 g/m², greater than or equalto about 60 g/m², greater than or equal to about 65 g/m², greater thanor equal to about 70 g/m², or greater than or equal to about 75 g/m².Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 40 g/m² and less than or equal to about80 g/m², greater than or equal to about 45 g/m² and less than or equalto about 62 g/m²). The basis weight may be determined according to thestandard ASTM D3776 (2013).

As noted above, the filter media, described herein, may be used for awide range of applications that may require a certain level ofparticulate efficiency. The particulate efficiency may be determined asa percentage of upstream monodisperse challenge particles in a feedstream retained by the filter media, or 100% minus a percentage ofparticles from a feed stream remaining in a permeate stream downstreamof the filter media. A beta ratio may be determined, as a number ofparticles upstream of a filter media divided by a number of particlesdownstream of the filter media. In some embodiments, particulateefficiency is measured, e.g., for flatsheet filter media, according toInternational Filter & Testing Services (IFTS) methodIFTS-FEEEIS-01:2013. Briefly, this test, when applied to flatsheetfilter media, is an efficiency test that involves challenging aflatsheet filter media with a challenge solution of monodisperseparticles of more than one size, with particles between or equal to 0.1microns and 1.5 microns in size, and measuring the number of particleshaving different sizes that are upstream and downstream of the flatsheetfilter media, where a flow rate of the challenge solution may be, e.g.,1 L/min. Filter media specimens used in these measurement tests may becircular in shape and have an effective area of 95 cm². The particulateefficiency measurements may be conducted at a constant flow rate of 1liter per minute through the media over the test period. The differencebetween the number of particles having a particle size that are upstreamof the flatsheet filter media (the upstream particle count) and thenumber of particles having the particle size that are downstream of theflatsheet filter media (the downstream particle count), divided by theupstream particle count, multiplied by 100, gives an efficiencypercentage of the media for the particle size, for example for 0.45micron particle size.

In some embodiments, the filter media may still have a relatively highparticulate efficiency. For instance, the particulate efficiency of thefilter media may be greater than conventional membrane filters. In someembodiments, the particulate efficiency for particles 0.45 micron insize or greater may be greater than or equal to about 99%, greater thanor equal to about 99.5%, greater than or equal to about 99.9%, greaterthan or equal to about 99.95%, or greater than or equal to about 99.99%.In some instances, the filter media and/or a fiber web may have aparticulate efficiency of less than 100%, less than or equal to about99.99%, or less than or equal to about 99.9%. Combinations of the abovereferenced ranges are also possible (e.g., greater than or equal toabout 99% and less than 100%, greater than or equal to about 99% andless than or equal to about 99.99%, greater than or equal to about 99%and less than or equal to about 99.9%). In some embodiments, particulateefficiency is measured, e.g., for flatsheet filter media, according toInternational Filter & Testing Services (IFTS) methodIFTS-FEEEIS-01:2013, monitoring particles 0.45 microns in size.

In some embodiments, the filter media may still have a relatively highparticulate efficiency. For instance, the particulate efficiency of thefilter media may be greater than conventional membrane filters. In someembodiments, the particulate efficiency for particles 0.3 micron in sizeor greater may be greater than or equal to about 99%, greater than orequal to about 99.5%, greater than or equal to about 99.9%, greater thanor equal to about 99.95%, or greater than or equal to about 99.99%, =.In some instances, the filter media and/or a fiber web may have aparticulate efficiency of less than 100%, less than or equal to about99.99%, or less than or equal to about 99.9%. Combinations of the abovereferenced ranges are also possible (e.g., greater than or equal toabout 99% and less than 100%, greater than or equal to about 99% andless than or equal to about 99.99%, greater than or equal to about 99%and less than or equal to about 99.9%). The particulate efficiency maybe measured, e.g., for flatsheet filter media, according toInternational Filter & Testing Services (IFTS) methodIFTS-FEEEIS-01:2013, monitoring particles 0.3 microns in size.

In some embodiments, the filter media may still have a relatively highparticulate efficiency. For instance, in some embodiments, theparticulate efficiency for particles 0.2 micron in size or greater maybe greater than or equal to about 80%, greater than or equal to about85%, greater than or equal to about 90%, greater than or equal to about95%, greater than or equal to about 97%, greater than equal to about99%, greater than or equal to about 99.9%, greater than or equal toabout 99.95%, or greater than or equal to about 99.99%. In someinstances, the filter media and/or a fiber web may have a particulateefficiency of less than 100%, less than or equal to about 99.99%, lessthan or equal to about 99.95%, less than or equal to about 99.9%, lessthan or equal to about 99.5%, less than or equal to about 99%, less thanor equal to about 97%, less than or equal to about 95%, less than orequal to about 90%, or less than or equal to about 85%. Combinations ofthe above referenced ranges are also possible (e.g., greater than orequal to about 80% and less than 100%, greater than or equal to about80% and less than or equal to about 99.9%, greater than or equal toabout 90% and less than or equal to about 99.99%). In some embodiments,particulate efficiency is measured, e.g., for flatsheet filter media,according to International Filter & Testing Services (IFTS) methodIFTS-FEEEIS-01:2013, monitoring particles 0.2 microns in size.

In some embodiments, a fiber web and/or filter media may be designed forsterile filtration. In some such embodiments, the particulate efficiencymay be very high (e.g., greater than or equal to about 99.999%). In someembodiments, the particulate efficiency of the filter media and/or afiber web may be expressed in terms of Log Reduction Value (i.e., LRV),which is a quantitative measure of microorganism retention by a fiberweb or filter media. LRV is the logarithm of a beta ratio and isexpressed as follows:LRV=Log {[CFU]challenge/[CFU]effluent]}wherein [CFU]challenge is the total number of bacteria in colony formingunits in the fluid before passage through the filter media and/or afiber web and [CFU]effluent is the total number of bacteria in colonyforming units in the fluid after passage through the filter media and/ora fiber web.

LRV may be determined using ASTM F838-05 (2005). A filter media isconsidered sterile when the [CFU]effluent is zero; however, if the[CFU]effluent is zero, one is used in the above equation to calculateLRV. Briefly, Brevumdimonas diminuta at a concentration of 10⁷ CFU/l cm²of sample area for a 76 cm² sample area may be used as the challenge.Therefore, the [CFU]challenge is 7.6×10⁸. An LRV of 8.88 is consideredsterile. In some embodiments, the filter media and/or a fiber web mayhave an LRV of greater than 4 LRV, e.g., between or equal to 4 LRV and 9LRV (e.g., 6 LRV). In some embodiments, the filter media and/or a fiberweb may have an LRV of 8.88. In some embodiments, the filter mediaand/or a fiber web may have an LRV of about 6. Such filter media couldbe used to reduce bioburden and remove some unwanted biologicalparticulates and thereby extend the service life of a final-stagefilter. Such filter media could be used as a final-stage filter tosupport industrial applications for the water, microelectronic,chemical, food and beverage and biomedical markets.

In some embodiments, the filter media described herein has a relativelyhigh water permeability. For instance, in some embodiments, the waterpermeability of the filter media and/or a fiber web may be greater thanor equal to about 2 ml/min·cm²·psi, greater than or equal to about 3ml/min·cm²·psi, greater than or equal to about 4 ml/min·cm²·psi, greaterthan or equal to about 5 ml/min·cm²·psi, greater than or equal to about6 ml/min·cm²·psi, greater than or equal to about 7 ml/min·cm²·psi, orgreater than or equal to about 8 ml/min·cm²·psi. In some instances, thewater permeability of the filter media may be less than or equal toabout 9 ml/min·cm²·psi, less than or equal to about 8 ml/min·cm²·psi,less than or equal to about 7 ml/min·cm²·psi, less than or equal toabout 6 ml/min·cm²·psi, less than or equal to about 5 ml/min·cm²·psi,less than or equal to about 4 ml/min·cm²·psi, or less than or equal toabout 3 ml/min·cm²·psi. It should be understood that all combinations ofthe above-referenced ranges are possible (e.g., greater than or equal toabout 2 ml/min·cm²·psi and less than or equal to about 9 ml/min·cm²·psi,greater than or equal to about 3 ml/min·cm²·psi and less than or equalto about 6 ml/min·cm²·psi). Other ranges are also possible.

Water permeability is the water flux divided by the pressure (e.g., 20psi) used to determine the water flow rate. Water flow rate is measuredby passing deionized water through a filter media or fiber web having aneffective filtration area of 12.5 cm² at a pressure of 20 psi until1,000 ml of water has been collected. The flow rate is determined bymeasuring the time until 1,000 ml of water has been collected. Waterflux is calculated by dividing the flow rate (ml/min) by a sampleeffective area (cm²) of the fiber web (i.e., the area exposed to fluidflow) and is expressed in ml/min-cm².

In some embodiments, the filter media may have a relatively high airpermeability. For instance, in some embodiments, the filter media mayhave an air permeability of greater than or equal to about 0.5 CFM,greater than or equal to about 1 CFM, greater than or equal to about 2CFM, greater than or equal to about 3 CFM, greater than or equal toabout 4 CFM, greater than or equal to about 5 CFM, greater than or equalto about 6 CFM, greater than or equal to about 7 CFM, greater than orequal to about 8 CFM, or greater than or equal to about 9 CFM. In someinstances, the air permeability may be less than or equal to about 10CFM, less than or equal to about 9 CFM, less than or equal to about 8CFM, less than or equal to about 7 CFM, less than or equal to about 6CFM, less than or equal to about 5 CFM, less than or equal to about 4CFM, less than or equal to about 3 CFM, or less than or equal to about 2CFM. All combinations of the above-referenced ranges are possible (e.g.,greater than about 0.5 CFM and less than or equal to about 10 CFM,greater than about 1 CFM and less than or equal to about 6 CFM). The airpermeability may be determined according to the standard ASTM D737-04(2016).

In some embodiments, the dirt holding capacity of the filter media isrelatively high. For instance, filter media, described herein, may havea significantly higher dirt holding capacity than membrane filtersand/or other conventional liquid filter media. In some embodiments, thedirt holding capacity of the filter media described herein is at least5% greater than (e.g., between about 5% and about 20% greater than)conventional membrane filters. In some embodiments, the relatively highdirt holding capacity may be due, at least in part, to the second fiberweb and/or third fiber web. In some cases, the second fiber web and/orthird fiber web may function as a pre-filter or capacity layer. In suchcases, the basis weight and pore size as well as other properties ofthese fiber webs are selected to enhance dirt holding capacity whilehaving relatively minimal or no adverse effects on one or moreproperties of the filter media that are important for a givenapplication, such as pore size distribution.

In some embodiments, the dirt holding capacity of the filter media maybe greater than or equal to about 20 mg/cm², greater than or equal toabout 22 mg/cm², greater than or equal to about 25 mg/cm², greater thanor equal to about 28 mg/cm², greater than or equal to about 30 mg/cm²,greater than or equal to about 32 mg/cm², greater than or equal to about35 mg/cm², or greater than or equal to about 38 mg/cm². In someinstances, the dirt holding capacity of the filter media may be lessthan or equal to about 40 mg/cm², less than or equal to about 38 mg/cm²,less than or equal to about 35 mg/cm², less than or equal to about 32mg/cm², less than or equal to about 30 mg/cm², less than or equal toabout 28 mg/cm², less than or equal to about 25 mg/cm², or less than orequal to about 22 mg/cm². Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 20 mg/cm² andless than or equal to about 40 mg/cm², greater than or equal to about 30mg/cm² and less than or equal to about 40 mg/cm²). Other values are alsopossible. The dirt holding capacity may be determined by using amodified version of EN-13443-2 (2005). Briefly, the dirt holdingcapacity test consisted of flowing through the filter media an aqueousdispersion of fine clay dust Jetfine 1A at a concentration of 100 mg/L.The flow rate was held constant at 1 liter per minute and the sampleeffective area was equal to 95 cm². The filtration test was stopped whenthe pressure drop generated across the media rises—due to clogging-up to2 bars. The weight gain due to fouling was determined by weighing thesample mass, in a dry state, before and after the filtration step.

In some embodiments, the pressure drop across the filter media may berelatively low. For instance, in some embodiments, the pressure dropacross the filter media may less than or equal to about 1 psi, less thanor equal to about 0.9 psi, less than or equal to about 0.8 psi, lessthan or equal to about 0.7 psi, less than or equal to about 0.6 psi,less than or equal to about 0.5 psi, less than or equal to about 0.4psi, less than or equal to about 0.3 psi, or less than or equal to about0.2 psi. In some instances, the filter media may have a pressure drop ofgreater than or equal to about 0.1 psi, greater than or equal to about0.2 psi, greater than or equal to about 0.3 psi, greater than or equalto about 0.4 psi, greater than or equal to about 0.5 psi, greater thanor equal to about 0.6 psi, greater than or equal to about 0.7 psi,greater than or equal to about 0.8 psi, or greater than or equal toabout 0.9 psi. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to about 0.1 psi and less than orequal to about 1 psi, greater than or equal to about 0.1 psi and lessthan or equal to about 0.5 psi. Other values of pressure drop are alsopossible. The flatsheet pressure drop can be measured using the NF X45-302 (2000) test method. The pressure drop was measured using cleanwater with a flow rate of 1 liter per minute through the filter media.

In some embodiments, the two or more fiber webs (e.g., first, second,and/or third fiber webs) in the filter media may have certain properties(e.g., water contact angle, surface energy) that are similar orsubstantially the same. The similarities between the webs may serve toenhance the permeability to certain fluids (e.g., water), the bondingbetween the fiber webs, and/or the structural stability of the filtermedia under various conditions (e.g., high temperature, high pressure,steam sterilization). For instance, a filter media comprising fiber webshaving substantially the same or similar water contact angle, criticalsurface tension, and/or critical wetting surface tension may exhibitenhanced wetting characteristics (e.g., fluid absorption andpermeability) and/or bonding compared to a filter media comprising firstand second fiber webs that are dissimilar with respect to theseproperties. In some such embodiments, two or more fiber webs (e.g.,first, second, and/or third fiber webs) may differ in water contactangle by less than or equal to about 20° (e.g., less than or equal toabout 15°), in critical surface tension by less than or equal to about15 dynes/cm (e.g., less than or equal to about 7 dynes/cm) and/or differin critical wetting surface tension by less than or equal to about 15dynes/cm (e.g., less than or equal to about 5 dynes/cm).

In some embodiments, two or more fiber webs (e.g., first, second, and/orthird fiber webs) may comprise substantially the same or similarmaterials, e.g., in order to enhance bonding between layers resultingfrom a heat lamination process. For example, the first, second, and/orthird fiber webs may comprise nylon, or any suitable material describedherein. In some embodiments, the first, second, and/or third fiber webscomprise a material (e.g., nylon) such that water has a relatively lowcontact angle with the fibers (e.g., less than 90 degrees, less than orequal to about 75 degrees, less than or equal to about 60 degrees, lessthan or equal to about 30 degrees) to facilitate high flow rate ofaqueous fluid through the filter media during filtration of the aqueousfluid by the filter media.

As used herein, the critical wetting surface tension of a fiber web orlayer (e.g., support layer) is defined as the mean of the surfacetension of the last liquid in a series that is absorbed by the fiber webor layer and the surface tension of the first liquid in a series that isnot absorbed by the fiber web or layer using the test described below.The critical wetting surface tension of a fiber web or layer may bedetermined by applying a series of liquids in a sequential manner (i.e.,from lowest surface tension to highest surface tension) to the surfaceof the fiber web or layer and observing the absorption or non-absorptionof each liquid as described in U.S. Pat. No. 4,880,548, which isincorporated by reference in its entirety, e.g., under “Wetting ofFibrous Media.” The technique involves placing ten drops of a firstliquid and 10 drops of a second liquid onto representative portions ofthe fiber web or layer and allowing the drops to stand for 10 minutes.The diameter of the droplets is between 3 mm and 5 mm. The two liquidsshould be selected so that the difference in surface tension betweenthem is about 2 dynes/cm. Absorption is defined as the wetting of afiber web or layer on its top and bottom surface by at least nine of theten drops within 10 minutes. Non-absorption is defined when at leastnine of the ten drops will not fully penetrate through the porous media,i.e., the bottom surface remains dry. Testing is continued using liquidsof successively higher or lower surface tension, until a pair has beenidentified, one absorbing and one non-absorbing, which are the mostclosely spaced in surface tension. The critical wetting surface tensionis then within that range and the average of the two surface tensions isused as a single number to specify the critical wetting surface tension.

In some embodiments, two or more fiber webs (e.g., first, second, and/orthird fiber webs) may differ in critical wetting surface tension by lessthan or equal to about 15 dynes/cm, less than or equal to about 12dynes/cm, less than or equal to about 10 dynes/cm, less than or equal toabout 8 dynes/cm, less than or equal to about 5 dynes/cm, less than orequal to about 3 dynes/cm, or less than or equal to about 1 dynes/cm andgreater than or equal to about 0 dynes/cm. In some embodiments, thecritical wetting surface tensions may be substantially the same. Incertain embodiments, the difference in critical wetting surface tensionmay be greater than about 0 dynes/cm.

In some embodiments, the critical wetting surface tension on the two ormore fiber webs (e.g., first, second, and/or third fiber webs) may begreater than or equal to about 10 dynes/cm, greater than or equal toabout 15 dynes/cm, greater than or equal to about 25 dynes/cm, greaterthan or equal to about 30 dynes/cm, greater than or equal to about 40dynes/cm, greater than or equal to about 50 dynes/cm, greater than orequal to about 60 dynes/cm, greater than or equal to about 70 dynes/cm,greater than or equal to about 80 dynes/cm, or greater than or equal toabout 90 dynes/cm.

In some instances, two or more fiber webs (e.g., first, second, and/orthird fiber webs) may have a critical wetting surface tension of lessthan or equal to about 110 dynes/cm, less than or equal to about 100dynes/cm, less than or equal to about 90 dynes/cm, less than or equal toabout 80 dynes/cm, less than or equal to about 72 dynes/cm, less than orequal to about 60 dynes/cm, less than or equal to about 50 dynes/cm,less than or equal to about 40 dynes/cm, less than or equal to about 30dynes/cm, or less than or equal to about 20 dynes/cm.

Combinations of the above-referenced ranges are possible (e.g., greaterthan or equal to about 10 dynes/cm and less than or equal to about 110dynes/cm, greater than or equal to about 25 dynes/cm and less than orequal to about 72 dynes/cm). Other values of the critical wettingsurface tension are possible.

In some embodiments, the weight percentage of the first fiber web in thefilter media may be less than or equal to about 10%, less than or equalto about 9%, less than or equal to about 8%, less than or equal to about7%, less than or equal to about 6%, less than or equal to about 5%, lessthan or equal to about 4%, less than or equal to about 3%, less than orequal to about 2%, or less than or equal to about 1%. In some instances,the weight percentage of the first fiber web in the filter media may begreater than or equal to about 0.8%, greater than or equal to about 1%,greater than or equal to about 1.2%, greater than or equal to about1.5%, greater than or equal to about 2%, greater than or equal to about3%, greater than or equal to about 4%, greater than or equal to about5%, greater than or equal to about 6%, greater than or equal to about7%, greater than or equal to about 8%, or greater than or equal to about9%. Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 0.8% and less than or equal to about 10%,greater than or equal to about 1.5% and less than or equal to about 4%).

In some embodiments, the weight percentage of the second fiber weband/or support layer in the filter media may be greater than or equal toabout 40%, greater than or equal to about 42%, greater than or equal toabout 45%, greater than or equal to about 48%, greater than or equal toabout 50%, greater than or equal to about 52%, greater than or equal toabout 55%, greater than or equal to about 58%, greater than or equal toabout 60%, greater than or equal to about 62%, or greater than or equalto about 65%. In some instances, the weight percentage of the secondfiber web in the filter media may be less than or equal to about 70%,less than or equal to about 68%, less than or equal to about 65%, lessthan or equal to about 60%, less than or equal to about 58%, less thanor equal to about 55%, less than or equal to about 52%, less than orequal to about 50%, or less than or equal to about 45%. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to about 40% and less than or equal to about 70%, greater than orequal to about 48% and less than or equal to about 65%).

In some embodiments, the weight percentage of the third fiber web in thefilter media may be greater than or equal to about 30%, greater than orequal to about 32%, greater than or equal to about 35%, greater than orequal to about 38%, greater than or equal to about 40%, greater than orequal to about 42%, greater than or equal to about 45%, greater than orequal to about 48%, greater than or equal to about 50%, greater than orequal to about 52%, or greater than or equal to about 55%. In someinstances, the weight percentage of the third fiber web in the filtermedia may be less than or equal to about 60%, less than or equal toabout 58%, less than or equal to about 55%, less than or equal to about52%, less than or equal to about 50%, less than or equal to about 48%,less than or equal to about 45%, less than or equal to about 42%, lessthan or equal to about 40%, less than or equal to about 380/%, or lessthan or equal to about 35%. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 30% and lessthan or equal to about 60%, greater than or equal to about 35% and lessthan or equal to about 48%).

*Fiber Webs/Filter Media—Synthetic Fibers

In general, any fiber web in the filter media, and accordingly thefilter media, may include any suitable fiber type. In some embodiments,one or more fiber web (e.g., first fiber web) and/or the entire filtermedia may include a single fiber type (e.g., synthetic fibers). Forexample, in certain embodiments, one or more fiber web and/or the entirefilter media may include synthetic fibers (e.g., nylon, silica, rayon,Lyocell, polyvinylidene fluoride, polytetrafluoroethylene,polypropylene, polyethersulfone, polyethylene terephthalate,polybutylene terephthalate) as described herein.

In some embodiments, the fibers in a fiber web (e.g., first fiber web,second fiber web) may have an average length which may depend on themethod of formation of the fibers. For instance, in some embodiments,fibers formed by an electrospinning (e.g., solvent electrospinning, meltelectrospinning), a melt-blown, a meltspun, or a centrifugal spinningprocess may be continuous (e.g., greater than about 5 cm, greater thanabout 50 cm, greater than about 200 cm).

In some embodiments, the filter media (e.g., filter media 100, filtermedia 120, and 140) may comprise synthetic fibers. For instance, in someembodiments, the efficiency layer (e.g., first fiber web) and/or thesupport layer (e.g., second fiber web) may comprise synthetic fibers.The synthetic fibers may have a relatively small average fiber diameter(e.g., less than or equal to about 2 microns). For instance, thesynthetic fibers in the first fiber web may have an average diameter ofless than or equal to about 0.5 microns (e.g., between about 0.05microns and 0.5 microns). In some embodiments, the synthetic fibers infirst fiber web 15, second fiber web 20, and/or filter media 10 may becontinuous fibers formed by any suitable process (e.g., a melt-blown, ameltspun, an electrospinning, a spunbond, a centrifugal spinningprocess). In certain embodiments, the synthetic fibers may be formed byan electrospinning process (e.g., melt electrospinning, solventelectrospinning). In other embodiments, the synthetic fibers may benon-continuous. In some embodiments, all of the fibers in the filtermedia are synthetic fibers. In certain embodiments, all of the fibers infirst fiber web 15 and/or second fiber web 20 are synthetic fibers. Insome such cases, all of the fibers in first fiber web 15 and/or secondfiber web 20 are continuous fibers.

Synthetic fibers may include any suitable type of synthetic polymer orother material. Examples of suitable synthetic fibers include polyimide,aliphatic polyamide (e.g., nylon 6), aromatic polyamide, polysulfone,cellulose acetate, polyether sulfone, polyaryl ether sulfone, modifiedpolysulfone polymers, modified polyethersulfone polymers, polymethylmethacrylate, polyacrylonitrile, polyurethane, poly(urea urethane),polybenzimidazole, polyetherimide, polyacrylonitrile, poly(ethyleneterephthalate), polypropylene, silicon dioxide (silica), regeneratedcellulose (e.g., Lyocell, rayon), carbon (e.g., derived from thepyrolysis of polyacrilonitrile), polyaniline, poly(ethylene oxide),poly(ethylene naphthalate), poly(butylene terephthalate), styrenebutadiene rubber, polystyrene, poly(vinyl chloride), poly(vinylalcohol), poly(vinylidene fluoride), poly(vinyl butylene) and copolymersor derivative compounds thereof, and combinations thereof. In someembodiments, the synthetic fibers are organic polymer fibers. Syntheticfibers may also include multi-component fibers (i.e., fibers havingmultiple compositions such as bicomponent fibers). In some cases,synthetic fibers may include electrospun (e.g., melt, solvent),meltblown, meltspun, or centrifugal spun fibers, which may be formed ofpolymers described herein (e.g., nylon, polyester, polypropylene). Insome embodiments, synthetic fibers may be electrospun fibers. The filtermedia, as well as each of the fiber webs within the filter media, mayalso include combinations of more than one type of synthetic fiber. Itshould be understood that other types of synthetic fiber types may alsobe used.

In some cases, the synthetic fibers (e.g., in the first and/or secondfiber webs) may be continuous (e.g., electrospun fibers, meltblownfibers, spunbond fibers, centrifugal spun fibers, etc.). For instance,synthetic fibers may have an average length of at least about 5 cm, atleast about 10 cm, at least about 15 cm, at least about 20 cm, at leastabout 50 cm, at least about 100 cm, at least about 200 cm, at leastabout 500 cm, at least about 700 cm, at least about 1000 cm, at leastabout 1500 cm, at least about 2000 cm, at least about 2500 cm, at leastabout 5000 cm, at least about 10000 cm; and/or less than or equal toabout 10000 cm, less than or equal to about 5000 cm, less than or equalto about 2500) cm, less than or equal to about 2000 cm, less than orequal to about 1000 cm, less than or equal to about 500 cm, or less thanor equal to about 200 cm. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to about 100 cm and lessthan or equal to about 2500 cm). Other values of average fiber lengthare also possible.

In other embodiments, the synthetic fibers are not continuous (e.g.,staple fibers). In general, synthetic non-continuous fibers may becharacterized as being shorter than continuous synthetic fibers. Forinstance, in some embodiments, synthetic fibers in one or more fiberwebs (e.g., second fiber web) in the filter media may have an averagelength of at least about 0.1 mm, at least about 0.5 mm, at least about1.0 mm, at least about 1.5 mm, at least about 2.0 mm, at least about 3.0mm, at least about 4.0 mm, at least about 5.0 mm, at least about 6.0 mm,at least about 7.0 mm, at least about 8.0 mm, at least about 9.0 mm, atleast about 10.0 mm, at least about 12.0 mm, at least about 15.0 mm;and/or less than or equal to about 15.0 mm, less than or equal to about12.0 mm, less than or equal to about 10.0 mm, less than or equal toabout 5.0 mm, less than or equal to about 4.0 mm, less than or equal toabout 1.0 mm, less than or equal to about 0.5 mm, or less than or equalto about 0.1 mm. Combinations of the above-referenced ranges are alsopossible (e.g., at least about 1.0 mm and less than or equal to about4.0 mm). Other values of average fiber length are also possible.

In some embodiments in which synthetic fibers are included in one ormore fiber webs and/or the entire filter media, the weight percentage ofsynthetic fibers in one or more fiber webs (e.g., first fiber web,second fiber web) and/or the entire filter media may be greater than orequal to about 1%, greater than or equal to about 20%, greater than orequal to about 40%, greater than or equal to about 60%, greater than orequal to about 75%, greater than or equal to about 90%, or greater thanor equal to about 95%.

In some instances, the weight percentage of synthetic fibers in thesecond fiber web may be less than or equal to about 100%, less than orequal to about 98%, less than or equal to about 85%, less than or equalto about 75%, less than or equal to about 50%, or less than or equal toabout 10%.

Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 75% and less than or equal to about100%). Other values of weight percentage of synthetic fibers are alsopossible. In some embodiments, one or more fiber webs (e.g., first fiberweb, second fiber web) and/or the entire filter media includes 100%synthetic fibers.

In one set of embodiments, one or more fiber webs (e.g., second fiberweb) in the filter media may include bicomponent fibers. The bicomponentfibers may comprise a thermoplastic polymer. Each component of thebicomponent fiber can have a different melting temperature. For example,the fibers can include a core and a sheath where the activationtemperature of the sheath is lower than the melting temperature of thecore. This allows the sheath to melt prior to the core, such that thesheath binds to other fibers in the fiber web, while the core maintainsits structural integrity. The core/sheath binder fibers can beconcentric or non-concentric. Other exemplary bicomponent fibers caninclude split fiber fibers, side-by-side fibers, and/or “island in thesea” fibers.

In some embodiments, bicomponent fibers may have an average length of atleast about 0.1 mm, at least about 0.5 mm, at least about 1.0 mm, atleast about 1.5 mm, at least about 2.0 mm, at least about 3.0 mm, atleast about 4.0 mm, at least about 5.0 mm, at least about 6.0 mm, atleast about 7.0 mm, at least about 8.0 mm, at least about 9.0 mm, atleast about 10.0 mm, at least about 12.0 mm, at least about 15.0 mm;and/or less than or equal to about 15.0 mm, less than or equal to about12.0 mm, less than or equal to about 10.0 mm, less than or equal toabout 5.0 mm, less than or equal to about 4.0 mm, less than or equal toabout 1.0 mm, less than or equal to about 0.5 mm, or less than or equalto about 0.1 mm. Combinations of the above-referenced ranges are alsopossible (e.g., at least about 1.0 mm and less than or equal to about4.0 mm). Other values of average fiber length are also possible.

In some embodiments in which bicomponent fibers are included in one ormore fiber webs (e.g., second fiber web) and/or the entire filter media,the weight percentage of bicomponent fibers in one or more fiber websand/or the entire filter media may be, for example, greater than orequal to about 1%, greater than or equal to about 5%, greater than orequal to about 10%, greater than or equal to about 15%, greater than orequal to about 30%, or greater than or equal to about 45%. In someinstances, the weight percentage of bicomponent fibers in one or morefiber webs and/or the entire filter media may be less than or equal toabout 70%, less than or equal to about 50%, less than or equal to about25%, less than or equal to about 10%, less than or equal to about 5%, orless than or equal to about 1%. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 30% andless than or equal to about 70%). Other values of weight percentage ofthe bicomponent fibers are also possible. In other embodiments, one ormore fiber webs (e.g., second fiber web) and/or the entire filter mediamay include 0% bicomponent fibers.

In some embodiments in which the second fiber web comprisesnon-continuous fibers, the second fiber web may comprise glass fibers.

In some embodiments, one or more layers (e.g., second fiber web, thirdfiber web) and/or the entire filter media is substantially free of glassfibers (e.g., less than 1 wt % glass fibers, between about 0 wt % andabout 1 wt % glass fibers). For instance, the first fiber web, secondfiber web, third fiber web and/or the entire filter media may include 0wt % glass fibers. Filter media and arrangements that are substantiallyfree of glass fibers may be advantageous for certain applications (e.g.,fuel-water separation, particulate separation in fuel systems), sinceglass fibers may shed and leach sodium ions (e.g., Na⁺) which can leadto physical abrasion and soap formation. For example, shedding of glassfibers may lead to the blockage of fuel injectors such as in highpressure common rail applications. In other embodiments, the secondlayer may optionally include glass fibers (e.g., microglass and/orchopped glass fibers).

In other embodiments, however, one or more layers and/or the entirefilter media may include glass fibers (e.g., microglass fibers, choppedstrand glass fibers, or a combination thereof). The average diameter ofglass fibers may be, for example, less than or equal to about 30microns, less than or equal to about 25 microns, less than or equal toabout 15 microns, less than or equal to about 12 microns, less than orequal to about 10 microns, less than or equal to about 9 microns, lessthan or equal to about 7 microns, less than or equal to about 5 microns,less than or equal to about 3 microns, or less than or equal to about 1micron. In some instances, the glass fibers may have an average fiberdiameter of greater than or equal to about 0.1 microns, greater than orequal to about 0.3 microns, greater than or equal to about 1 micron,greater than or equal to about 3 microns, or greater than equal to about7 microns greater than or equal to about 9 microns, greater than orequal to about 11 microns, or greater than or equal to about 20 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to about 0.1 microns and less than or equal toabout 9 microns). Other values of average fiber diameter are alsopossible.

In some embodiments, the weight percentage of the glass fibers may begreater than or equal to about 0 wt %, greater than or equal to about 2wt %, greater than or equal to about 5 wt %, greater than or equal toabout 10 wt %, greater than or equal to about 15 wt %, greater than orequal to about 25 wt %, greater than or equal to about 35 wt %, greaterthan or equal to about 50 wt %, greater than or equal to about 65 wt %,or greater than or equal to about 80 wt %. In some instances, the weightpercentage of the glass fibers in the layer may be less than or equal toabout 100 wt %, less than or equal to about 98 wt %, less than or equalto about 95 wt %, less than or equal to about 90 wt %, less than orequal to about 80 wt %, less than or equal to about 65 wt %, less thanor equal to about 50 wt %, less than or equal to about 35 wt %, lessthan or equal to about 25 wt %, less than or equal to about 20 wt %,less than or equal to about 15 wt %, less than or equal to about 10 wt%, less than or equal to about 5 wt %, less than or equal to about 2 wt%, or less than or equal to about 1 wt %. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0 wt % and less than or equal to about 10 wt %, greater than orequal to about 2 wt % and less than or equal to about 100 wt %). In someembodiments, weight percentage of the glass fibers may be less than orequal to about 5 wt. % (e.g., 0 wt. %). In other embodiments, weightpercentage of the glass fibers may be greater than or equal to about 90wt. % (e.g., 100 wt. %). Other values of weight percentage of the glassin a layer are also possible. In some embodiments, a layer or the filtermedia includes the above-noted ranges of glass fibers with respect tothe total weight of fibers in the layer or filter media, respectively.In some embodiments, the above weight percentages are based on theweight of the total dry solids of the layer.

In some embodiments in which the second fiber web comprisesnon-continuous fibers, the second fiber web may comprise fibrillatedfibers (e.g., fibrillated lyocell fibers, fibrillated acrylic fibers).

In some embodiments, the fibers in one or more layers (e.g., secondfiber web, third fiber web) and/or the filter media may comprisefibrillated fibers. As known to those of ordinary skill in the art, afibrillated fiber includes a parent fiber that branches into smallerdiameter fibrils, which can, in some instances, branch further out intoeven smaller diameter fibrils with further branching also beingpossible. The branched nature of the fibrils leads to a high surfacearea and can increase the number of contact points between thefibrillated fibers and the fibers in the fiber web. Such an increase inpoints of contact between the fibrillated fibers and other fibers and/orcomponents of the web may contribute to enhancing mechanical properties(e.g., flexibility, strength) and/or filtration performance propertiesof the fiber web.

Examples of fibrillated fibers, include, but are not limited to,fibrillated regenerated cellulose (e.g., rayon, Lyocell),microfibrillated cellulose, nanofibrillated cellulose, fibrillatedsynthetic fibers, including nanofibrillated synthetic fibers (e.g.,fibrillated fibers formed of synthetic polymers such as polyester,polyamide, polyaramid, para-aramid, meta-aramid, polyimide,polyethylene, polypropylene, polyether ether ketone, polyethyleneterephthalate, polyolefin, nylon, and/or acrylics), and fibrillatednatural fibers (e.g., hardwood, softwood). Regardless of the type offibrillated fibers, the weight percentage of fibrillated fibers in oneor more layers (e.g., second fiber web, third fiber web) and/or theentire filter media may be greater than or equal to about 0 wt %,greater than or equal to about 1 wt %, greater than or equal to about 5wt %, greater than or equal to about 10 wt %, greater than or equal toabout 20 wt %, greater than or equal to about 30 wt %, greater than orequal to about 40 wt %, greater than or equal to about 50 wt %, greaterthan or equal to about 60 wt %, greater than or equal to about 70 wt %,or greater than or equal to about 80 wt %, e.g., based on the totalweight of fibers in the layer or media. In some instances, the weightpercentage of the fibrillated fibers in one or more layers and/or theentire filter media may be less than or equal to about 100 wt %, lessthan or equal to about 98 wt %, less than or equal to about 95 wt %,less than or equal to about 90 wt %, less than or equal to about 80 wt%, less than or equal to about 70 wt %, less than or equal to about 60wt %, less than or equal to about 50 wt %, less than or equal to about40 wt %, less than or equal to about 30 wt %, less than or equal toabout 20 wt %, or less than or equal to about 10%, e.g., based on thetotal weight of fibers in the layer or media. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 0 wt %, and less than or equal to about 100 wt %, greater thanor equal to about 0 wt %, and less than or equal to about 80 wt %).Other values of weight percentage of the fibrillated fibers in one ormore layers and/or the entire filter media are also possible. In someembodiments, a layer or the filter media may include 0 wt %/fibrillatedfibers. In some embodiments, a layer (e.g., second fiber web, thirdfiber web) of the filter media may include greater than or equal toabout 90 wt. % (e.g., 100 wt. %) fibrillated fibers. For instance, thesecond layer may comprise 100 wt. % fibrillated fibers. In someembodiments, a layer or the filter media includes the above-noted rangesof fibrillated fibers with respect to the total weight of fibers in thelayer or filter media, respectively. In some embodiments, the aboveweight percentages are based on the weight of the total dry solids ofthe layer or filter media (including any resins).

In some embodiments the parent fibers may have an average diameter inthe micron range. For example, the parent fibers may have an averagediameter of greater than or equal to about 1 micron, greater than orequal to about 5 microns, greater than or equal to about 10 microns,greater than or equal to about 20 microns, greater than or equal toabout 30 microns, greater than or equal to about 40 microns, greaterthan or equal to about 50 microns, greater than or equal to about 60microns, or greater than or equal to about 70 microns. In someembodiments, the parent fibers may have an average diameter of less thanor equal to about 75 microns, less than or equal to about 55 microns,less than or equal to about 35 microns, less than or equal to about 25microns, less than or equal to about 15 microns, less than or equal toabout 10 microns, or less than or equal to about 5 microns. Combinationsof the above referenced ranges are also possible (e.g., parent fibershaving an average diameter of greater than or equal to about 1 micronand less than or equal to about 25 microns). Other ranges are alsopossible.

In other embodiments, the parent fibers may have an average diameter inthe nanometer range. For instance in, some embodiments, the parentfibers may have an average diameter of less than about 1 micron, lessthan or equal to about 0.8 microns, less than or equal to about 0.5microns, less than or equal to about 0.1 microns, less than or equal toabout 0.05 microns, less than or equal to about 0.02 microns, less thanor equal to about 0.01 microns, or less than or equal to about 0.005microns. In some embodiments, the parent fibers may have an averagediameter of greater than or equal to about 0.003 microns, greater thanor equal to about 0.004 micron, greater than or equal to about 0.01microns, greater than or equal to about 0.05 microns, greater than orequal to about 0.1 microns, or greater than or equal to about 0.5microns. Combinations of the above referenced ranges are also possible(e.g., parent fibers having an average diameter of greater than or equalto about 0.004 microns and less than about or equal to about 0.02microns). Other ranges are also possible.

The average diameter of the fibrils is generally less than the averagediameter of the parent fibers. Depending on the average diameter of theparent fibers, in some embodiments, the fibrils may have an averagediameter of less than or equal to about 25 microns, less than or equalto about 20 microns, less than or equal to about 10 microns, less thanor equal to about 5 microns, less than or equal to about 1 micron, lessthan or equal to about 0.5 microns, less than or equal to about 0.1microns, less than or equal to about 0.05 microns, or less than or equalto about 0.01 microns. In some embodiments the fibrils may have anaverage diameter of greater than or equal to about 0.003 microns,greater than or equal to about 0.01 micron, greater than or equal toabout 0.05 microns, greater than or equal to about 0.1 microns, greaterthan or equal to about 0.5 microns greater than or equal to about 1micron, greater than or equal to about 5 microns, greater than or equalto about 10 microns, or greater than or equal to about 20 microns.Combinations of the above referenced ranges are also possible (e.g.,fibrils having an average diameter of greater than or equal to about0.01 microns and less than or equal to about 20 microns). Other rangesare also possible.

The level of fibrillation may be measured according to any number ofsuitable methods. For example, the level of fibrillation of thefibrillated fibers can be measured according to a Canadian StandardFreeness (CSF) test, specified by TAPPI test method T 227 om 09 (2009)Freeness of pulp. The test can provide an average CSF value.

In some embodiments, the average CSF value of the fibrillated fibersused in one or more layers may vary between about 5 mL and about 750 mL.In certain embodiments, the average CSF value of the fibrillated fibersused one or more layers may be greater than or equal to 1 mL, greaterthan or equal to about 10 mL, greater than or equal to about 20 mL,greater than or equal to about 35 mL, greater than or equal to about 45mL, greater than or equal to about 50 mL, greater than or equal to about65 mL, greater than or equal to about 70 mL, greater than or equal toabout 75 mL, greater than or equal to about 80 mL, greater than or equalto about 100 mL, greater than or equal to about 150 mL, greater than orequal to about 175 mL, greater than or equal to about 200 mL, greaterthan or equal to about 250 mL, greater than or equal to about 300 mL,greater than or equal to about 350 mL, greater than or equal to about500 mL, greater than or equal to about 600 mL, greater than or equal toabout 650 mL, greater than or equal to about 700 mL, or greater than orequal to about 750 mL.

In some embodiments, the average CSF value of the fibrillated fibersused in one or more layers may be less than or equal to about 800 mL,less than or equal to about 750 mL, less than or equal to about 700 mL,less than or equal to about 650 mL, less than or equal to about 600 mL,less than or equal to about 550 mL, less than or equal to about 500 mL,less than or equal to about 450 mL, less than or equal to about 400 mL,less than or equal to about 350 mL, less than or equal to about 300 mL,less than or equal to about 250 mL, less than or equal to about 225 mL,less than or equal to about 200 mL, less than or equal to about 150 mL,less than or equal to about 100 mL, less than or equal to about 90 mL,less than or equal to about 85 mL, less than or equal to about 70 mL,less than or equal to about 50 mL, less than or equal to about 40 mL,less than or equal to about 25 mL, less than or equal to about 10 mL, orless than or equal to about 5 mL. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to about 10 mL andless than or equal to about 300 mL). Other ranges are also possible. Theaverage CSF value of the fibrillated fibers used in one or more layersmay be based on one type of fibrillated fiber or more than one type offibrillated fiber.

In some embodiments, one or more fiber webs and/or the entire filtermedia, in addition to a plurality of fibers, may also include othercomponents, such as a resin, surface treatments, and/or additives. Ingeneral, any suitable resin may be used to achieve the desiredproperties. For example, the resin may be polymeric, water-based,solvent-based, dry strength, and/or wet strength. Typically, anyadditional components are present in limited amounts.

In some embodiments, at least a portion of the fibers of one or morefiber web may be coated with a resin without substantially blocking thepores of the fiber web. In some embodiments, one or more fiber webs orthe entire filter media described herein include a resin.

In some embodiments, the resin may be a binder resin. The binder resinis not in fiber form and is to be distinguished from binder fiber (e.g.,multi-component fiber) described above. In general, the binder resin mayhave any suitable composition. For example, the binder resin maycomprise a thermoplastic (e.g., acrylic, polyvinylacetate, polyester,polyamide), a thermoset (e.g., epoxy, phenolic resin), or a combinationthereof. In some cases, a binder resin includes one or more of a vinylacetate resin, an epoxy resin, a polyester resin, a copolyester resin, apolyvinyl alcohol resin, an acrylic resin such as a styrene acrylicresin, and a phenolic resin. Other resins are also possible.

As described further below, the resin may be added to the fibers in anysuitable manner including, for example, in the wet state. In someembodiments, the resin coats the fibers and is used to adhere fibers toeach other to facilitate adhesion between the fibers. Any suitablemethod and equipment may be used to coat the fibers, for example, usingcurtain coating, gravure coating, melt coating, dip coating, knife rollcoating, or spin coating, amongst others. In some embodiments, thebinder is precipitated when added to the fiber blend. When appropriate,any suitable precipitating agent (e.g., Epichlorohydrin, fluorocarbon)may be provided to the fibers, for example, by injection into the blend.In some embodiments, upon addition to the fibers, the resin is added ina manner such that one or more fiber web or the entire filter media isimpregnated with the resin (e.g., the resin permeates throughout). In amulti-fiber web, a resin may be added to each of the fiber websseparately prior to combining the fiber webs, or the resin may be addedto the fiber web after combining the fiber webs. In some embodiments,resin is added to the fibers while in a dry state, for example, byspraying or saturation impregnation, or any of the above methods. Inother embodiments, a resin is added to a wet fiber web.

Filter media described herein may be produced using suitable processes,such as using a non-wet laid or a wet laid process. In some embodiments,a fiber web and/or the filter media described herein may be producedusing a non-wet laid process, such as blowing or spinning process. Insome embodiments, a fiber web (e.g., first fiber web, second fiber web)and/or the entire filter media may be formed by an electrospinningprocess. In some embodiments, electrospinning utilizes a high voltagedifferential to generate a fine jet of polymer solution from bulkpolymer solution. The jet forms as the polymer is charged by thepotential and electrostatic repulsion forces overcome the surfacetension of the solution. The jet gets drawn into a fine fiber under theeffect of repulsive electrical forces applied to the solution. The jetdries in flight and is collected on a grounded collector. The rapidsolvent evaporation during this process leads to the formation ofpolymeric nanofiber which are randomly arranged into a web. In someembodiments, electrospun fibers are made using non-melt fiberizationprocesses. Electrospun fibers can be made with any suitable polymersincluding but not limiting to, organic polymers, inorganic material(e.g., silica), hybrid polymers, and any combination thereof. In someembodiments, the synthetic fibers, described herein, may be formed froman electrospinning process.

In certain embodiments, a fiber web (e.g., first fiber web, second fiberweb) and/or the entire filter media may be formed by a meltblowingsystem, such as the meltblown system described in U.S. Publication No.2009/0120048, filed Nov. 7, 2008, and entitled “Meltblown FilterMedium”, and U.S. Publication No. 2012-0152824, filed Dec. 17, 2010, andentitled, “Fine Fiber Filter Media and Processes”, each of which isincorporated herein by reference in its entirety for all purposes. Incertain embodiments, a fiber web (e.g., first fiber web, second fiberweb) and/or the entire filter media may be formed by a meltspinning or acentrifugal spinning process.

In some embodiments, a non-wet laid process, such as an air laid orcarding process, may be used to form one or more fiber webs. Forexample, in an air laid process, synthetic fibers may be mixed, whileair is blown onto a conveyor. In a carding process, in some embodiments,the fibers are manipulated by rollers and extensions (e.g., hooks,needles) associated with the rollers. In some cases, forming the fiberwebs through a non-wet laid process may be more suitable for theproduction of a highly porous media. In some embodiments, a non-wet laidprocess (e.g., electrospun, meltblown) may be used to form the firstfiber web and a wet laid process may be used to form the second fiberweb. The first fiber web and the second fiber web may be combined usingany suitable process (e.g., lamination, calendering, smooth rollcalendering).

In some embodiments, a fiber web and/or the filter media describedherein may be produced using a wet laid process. In general, a wet laidprocess involves mixing together of fibers of one or more type; forexample, polymeric staple fibers of one type may be mixed together withpolymeric staple fibers of another type, and/or with fibers of adifferent type (e.g., synthetic fibers and/or glass fibers), to providea fiber slurry. The slurry may be, for example, an aqueous-based slurry.In certain embodiments, fibers, are optionally stored separately, or incombination, in various holding tanks prior to being mixed together(e.g., to achieve a greater degree of uniformity in the mixture).

During or after formation of a filter media, the filter media may befurther processed according to a variety of known techniques. Forinstance, a coating method may be used to include a resin in the filtermedia. Optionally, additional fiber webs can be formed and/or added to afilter media using processes such as lamination, co-pleating, orcollation. For example, in some cases, two fiber webs (e.g., first fiberweb and the second fiber web) are formed into a composite article by awet laid process as described above, and the composite article is thencombined with a third fiber web by any suitable process (e.g.,lamination, co-pleating, or collation). It can be appreciated that afilter media or a composite article formed by the processes describedherein may be suitably tailored not only based on the components of eachfiber web, but also according to the effect of using multiple fiber websof varying properties in appropriate combination to form filter mediahaving the characteristics described herein.

As described herein, in some embodiments two or more fiber webs of thefilter media (e.g., first fiber web and the third fiber web) may beformed separately and bonded by any suitable method such as lamination,collation, or by use of adhesives. The two or more fiber webs may beformed using different processes, or the same process. For example, eachof the fiber webs may be independently formed by a non-wet laid process(e.g., meltblown process, melt spinning process, centrifugal spinningprocess, electrospinning process, dry laid process, air laid process), awet laid process, or any other suitable process.

Different fiber webs may be adhered together by any suitable method. Forinstance, fiber webs may be adhered using compressive techniques (e.g.,lamination). Fiber webs may also be adhered by chemical bonding,adhesive and/or melt-bonded to one another on either side.

Lamination may involve, for example, compressing two or more fiber webs(e.g., first and second fiber webs) together using a flatbed laminatoror any other suitable device at a particular pressure and temperaturefor a certain residence time (i.e., the amount of time spent underpressure and heat). For instance, the pressure may be between about 40psi to about 60 psi (e.g., between about 40 psi to about 55 psi, betweenabout 40 psi to about 50 psi, between about 45 psi to about 55 psi,between about 45 and 60 psi, between about 50 psi and about 60 psi); thetemperature may be between about 100° C. and about 200° C. (e.g.,between about 100° C. and about 175° C., between about 100° C. and about150° C., or between about 100° C. and about 125° C. between about 125°C. and about 200° C., between about 150° C. and about 200° C., betweenabout 175° C. and about 200° C.); the residence time between about 1second to about 60 seconds (e.g., between about 1 second to about 30seconds, between about 10 second to about 25 seconds, or between about20 seconds and about 40 seconds); and/or the line speed between about 5m/min and about 20 m/min (e.g., between about 8 m/min and about 20m/min, between about 10 m/min and about 20 m/min, between about 12 m/minand about 20 m/min, between about 15 m/min and about 20 m/min, betweenabout 5 m/min and about 18 m/min, between about 5 m/min and about 15m/min, between about 5 m/min and about 12 m/min. between about 5 m/minand about 10 m/min). Other ranges for pressure, temperature, andresidence time are also possible.

In some embodiments, the filter media may include a first fiber webformed via an electrospinning process adhered (e.g., adhesively) to asecond fiber web formed via another process (e.g., meltblowing process).For instance, the first fiber web (e.g., electrospun fiber web) may beadhesively bound to a second fiber web (e.g., meltblown fiber web).Non-limiting example of suitable adhesive include acrylic copolymers,ethyl vinyl acetate (EVA), copolyesters, polyolefins, polyamides,polyurethanes, styrene block copolymers, thermoplastic elastomers,polycarbonates, silicones, and combinations thereof. Adhesives can beapplied using different methods, such as spray coating (e.g., solutionspraying if solvent or water based adhesives are used or melt sprayingif hot melt adhesive is used), dip coating, kiss roll, knife coating,and gravure coating. In some embodiments, a first fiber web (e.g.,electrospun fiber web) and a second fiber web (e.g., meltblown fiberweb) may be adhesively bound using a polymeric adhesive (e.g., acryliccopolymer) applied via spray coating. For example, an electrospun fiberweb (e.g., comprising nylon fibers) and a meltblown fiber web (e.g.,comprising polypropylene fibers) may be adhesively bound using apolymeric adhesive (e.g., acrylic copolymer) applied via spray coating.

In some embodiments, at least a portion of a surface of the first fiberweb may be bonded (e.g., via lamination, via adhesive) to a third fiberweb formed via a meltblowing, wetlaid, air laid, force spinning,electrospinning, or electroblowing process. In some cases, the thirdfiber web may be bonded to a surface of the first fiber web to form thefilter media. In some embodiments, the bonding process does notsignificantly change the pore characteristics of the first fiber web.For instance, one or more pore properties (e.g., maximum pore size, fullwidth at half maximum, mean flow pore size, ratio of maximum pore sizeto mean flow pore size) of the filter media may be within about 0% (nochange) to 100% (100% change) of the value of the same pore property ofthe first fiber web prior to the bonding step, or in some embodimentswithin 0% to 50% (e.g., within 0% to 25%, within 0% to 10%) of the valueof the same pore property of the first fiber web prior to the bondingstep. As an example, a first fiber web adjacent to a second fiber web,described herein, may have a maximum pore size of greater than or equalto about 0.1 microns and less than or equal to about 1.0 micron and aratio of maximum pore size to mean pore size of less than or equal toabout 2.5 prior to the bonding step. The filter media may have a maximumpore size and/or a ratio of maximum pore size to mean pore size that iswithin about 50% of the maximum pore size and/or a ratio of maximum poresize to mean pore size of the first fiber web prior to the bonding step.

As described herein, in some embodiments, the second fiber web and/orsupport layer may be calendered. In general, the second fiber web iscalendered prior to contact with another fiber web (e.g., first fiberweb). For example, first fiber web may be formed on a calendered secondfiber web. In such cases, the first fiber web is uncalendered and thesecond fiber web is calendered. In some embodiments, the support layer(e.g., second fiber web and fourth fiber web) is calendered prior tocontact with another fiber web (e.g., first fiber web). For instance, inembodiments in which the support layer comprises two or more fiber websas described above with respect to FIG. 1C, the support layer maycomprise two or more calendered fiber webs. For example, the supportlayer may comprise a meltblown fiber web and a spunbond fiber web thatare calendered prior to formation of the first fiber web on themeltblown fiber web.

The calendering process may involve compressing one or more fiber webs(e.g., second fiber web, second and fourth fiber webs) using calenderrolls under a particular pressure, temperature, and line speed. Forinstance, the pressure may be between about 500 psi to about 800 psi(e.g., between about 550 psi to about 750 psi, between about 550 psi toabout 700 psi, between about 550 psi to about 650 psi, between about 550and 600 psi, between about 600 psi and about 750 psi, between about 600psi and about 700 psi, between about 650 psi and about 750 psi, betweenabout 700 psi and about 750 psi); the temperature may be between about40° C. and about 120° C. (e.g., between about 40° C. and about 85° C.,between about 50° C. and about 85° C., between about 60° C. and about85° C., between about 65° C. and about 75° C., between about 70° C. andabout 85° C., between about 35° C. and about 80° C., between about 35°C. and about 70° C. between about 35° C. and about 60° C., between about35° C. and about 50° C.); and/or the line speed may be between about 5ft/min to about 100 ft/min (e.g., between about 5 ft/min to about 80ft/min, between about 10 ft/min to about 50 ft/min, between about 15ft/min to about 100 ft/min, between about 15 ft/min to about 25 ft/min,or between about 20 ft/min to about 90 ft/min). Other ranges forpressure, temperature, and line speed are also possible.

In some embodiments, further processing may involve pleating the filtermedia. For instance, two fiber webs may be joined by a co-pleatingprocess. In some cases, the filter media, or various fiber webs thereof,may be suitably pleated by forming score lines at appropriately spaceddistances apart from one another, allowing the filter media to befolded. In some cases, one fiber web can be wrapped around a pleatedfiber web. It should be appreciated that any suitable pleating techniquemay be used.

In some embodiments, a filter media can be post-processed such assubjected to a corrugation process to increase surface area within theweb. In other embodiments, a filter media may be embossed.

In some embodiments, a fiber web, a layer, and/or a filter mediadescribed herein is not embossed.

The filter media may include any suitable number of fiber webs, e.g., atleast 2, at least 3, at least 4, at least 5, at least 6, at least 7fiber webs. In some embodiments, the filter media may include up to 20fiber webs.

In some embodiments, a fiber web described herein may be a non-wovenweb. A non-woven web may include non-oriented fibers (e.g., a randomarrangement of fibers within the web). Examples of non-woven websinclude webs made by wet-laid or non-wet laid processes as describedherein. Non-woven webs also include papers such as cellulose-based webs.

Filter media described herein may be used in an overall filtrationarrangement or filter element. In some such embodiments, one or moreadditional fiber webs or components are included with the filter media.It should be appreciated that the filter media may include other partsin addition to the one or more fiber webs described herein. In someembodiments, further processing includes incorporation of one or morestructural features and/or stiffening elements. For instance, the filtermedia may be combined with additional structural features such aspolymeric and/or metallic meshes. In one embodiment, a screen backingmay be disposed on the filter media, providing for further stiffness. Insome cases, a screen backing may aid in retaining the pleatedconfiguration. For example, a screen backing may be an expanded metalwire or an extruded plastic mesh.

In some embodiments, filter media can be incorporated into a variety offilter elements for use in various filtering applications. Exemplarytypes of filters include bioprocessing filters, chemical processingfilters, industrial processing filters, medical filters (e.g., filtersfor blood), vent filters, air filters, and water filters. The filtermedia may be suitable for filtering gases or liquids. The water and/orair filters may be used for the removal of microorganisms, virusparticles, and/or other contaminants. For instance, filter mediasuitable for water filtration may be used for the treatment of municipalwater, residential water, and/or industrial water (e.g., mining water,cooling tower/boiler's water, nuclear water, ultra-pure water productionfor the semiconductor and biopharmaceutical industries).

Filter elements can also be in any suitable form, such as pleatedfilter, capsules, spiral wound elements, plate and frame devices, flatsheet modules, vessel bags, disc tube units, radial filter elements,panel filter elements, or channel flow elements. A radial filter elementcan include pleated filter media that are constrained within two openwire meshes in a cylindrical shape. During use, fluids can flow from theoutside through the pleated media to the inside of the radial element.

In some cases, the filter element includes a housing that may bedisposed around the filter media. The housing can have variousconfigurations, with the configurations varying based on the intendedapplication. In some embodiments, the housing may be formed of a framethat is disposed around the perimeter of the filter media. For example,the frame may be thermally sealed around the perimeter. In some cases,the frame has a generally rectangular configuration surrounding all foursides of a generally rectangular filter media. The frame may be formedfrom various materials, including for example, metal, polymers, or anycombination of suitable materials. The filter elements may also includea variety of other features known in the art, such as stabilizingfeatures for stabilizing the filter media relative to the frame,spacers, or any other appropriate feature.

The filter elements may have one or more properties that hassubstantially the same or improved values as those noted above inconnection with the filter media. For example, the above-noted waterpermeability, filtration efficiency, maximum pore size, mean pore size,and/or pore size distribution may also be found in filter elements. Insome embodiments, cartridge elements (e.g., standard 10″ elements) areprovided.

In some embodiments, a cartridge element comprises a filter media. Insome embodiments, the filter media is pleated, having a pleat height ofbetween or equal to 0.1 cm and 10 cm (e.g., between or equal to 0.5 cmand 2 cm. e.g., 1.27 cm). In some embodiments, a cartridge elementfurther comprises one or more scrim layers (e.g., two, three, or morescrim layers) adjacent to the filter media. In some embodiments, thefilter media and the one or more scrim layers (e.g., pleated together)are configured together as an open-ended cylinder. In some embodiments,the cartridge element further comprises a cartridge housing in which thefilter media and/or one or more scrim layers is located, e.g., havingsealed end caps enclosing the filter media and/or one or more scrimlayers.

In some embodiments, a method of making a cartridge element is provided.In some embodiments, the method comprises feeding a filter mediadescribed herein, in roll format together with a layer of scrim (e.g.,polypropylene scrim) on the upstream and two layers of scrim (e.g.,polypropylene scrim) on the downstream side, to a blade pleater tocreate 1.27 cm pleat height across the media and the scrim layers. Insome embodiments, the method further comprises cutting the pleatedscrim-supported media to an appropriate length and seaming the media,e.g., to form an open-ended cylinder. In some embodiments, the methodfurther comprises inserting the pleated media cylinder into a cartridgehousing and enclosing the cylinder, e.g., by means of heat sealing theend caps of the housing.

In some embodiments, the filter element (e.g., cartridge element) maystill have a relatively high particulate efficiency. For instance, insome embodiments, the particulate efficiency for particles 0.45 micronsin size or greater may be greater than or equal to about 98%, greaterthan or equal to about 98.5%, greater than or equal to about 996,greater than or equal to about 99.5%, greater than or equal to about99.9%, or greater than or equal to about 99.99%. In some instances, thefilter element may have a particulate efficiency of less than 100%, lessthan or equal to about 99.99%, less than or equal to about 99.9%, orless than or equal to about 99%. Combinations of the above referencedranges are also possible (e.g., greater than or equal to about 98% andless than 100%, greater than or equal to about 98% and less than orequal to about 99.99%, greater than or equal to about 99% and less thanor equal to about 99.9%). The particulate efficiency may be measured,e.g., for a filter element (e.g., cartridge element), according to IFTSmethod IFTS-FEEEIS-01:2013, monitoring particles 0.45 microns in size.The efficiency may be measured as described above except that the flowrate of a challenge solution may differ between flatsheet filter mediaand cartridge elements. In the case of flatsheet filter media, in somecases, a flow rate of a challenge solution may be 1 L/min. whereas aflow rate of a challenge solution for a cartridge element may be 15L/min.

In some embodiments, the filter element may still have a relatively highparticulate efficiency. For instance, in some embodiments, theparticulate efficiency for particles 0.3 microns in size or greater maybe greater than or equal to about 98%, greater than or equal to about98.5%, greater than or equal to about 99%, greater than or equal toabout 99.5%, greater than or equal to about 99.9%, or greater than orequal to about 99.99%. In some instances, the filter element may have aparticulate efficiency of less than 100%, less than or equal to about99.99%, less than or equal to about 99.9%, or less than or equal toabout 99%. Combinations of the above referenced ranges are also possible(e.g., greater than or equal to about 98% and less than 100%, greaterthan or equal to about 98% and less than or equal to about 99.99%,greater than or equal to about 99% and less than or equal to about99.9%). The particulate efficiency may be measured, e.g., for a filterelement (e.g., cartridge element), according to IFTS methodIFTS-FEEEIS-01:2013, monitoring particles 0.3 microns in size.

In some embodiments, the filter element may still have a relatively highparticulate efficiency. For instance, in some embodiments, theparticulate efficiency for particles 0.2 microns in size or greater maybe greater than or equal to about 90%, greater than or equal to about92%, greater than or equal to about 95%, greater than or equal to about98%, greater than or equal to about 99%, greater than or equal to about99.9%, or greater than or equal to about 99.99%. In some instances, thefilter element may have a particulate efficiency of less than 100%, lessthan or equal to about 99.99%, less than or to equal to about 99.9%,less than or equal to about 99%, less than or equal to about 97%, orless than or equal to about 95%. Combinations of the above referencedranges are also possible (e.g., greater than or equal to about 90% andless than 100%, greater than or equal to about 90% and less than orequal to about 99.99%, greater than or equal to about 90% and less thanor equal to about 99.9%). The particulate efficiency may be measured,e.g., for a filter element (e.g., cartridge element), according to IFTSmethod IFTS-FEEEIS-01:2013, monitoring particles 0.2 microns in size.

In some embodiments, the dirt holding capacity of the filter element maybe greater than or equal to about 60 mg/cm², greater than or equal toabout 65 mg/cm², greater than or equal to about 70 mg/cm², greater thanor equal to about 75 mg/cm², greater than or equal to about 80 mg/cm²,greater than or equal to about 85 mg/cm², greater than or equal to about90 mg/cm², or greater than or equal to about 95 mg/cm². In someinstances, the dirt holding capacity of the filter element may be lessthan or equal to about 100 mg/cm², less than or equal to about 95mg/cm², less than or equal to about 90 mg/cm², less than or equal toabout 85 mg/cm², less than or equal to about 80 mg/cm², less than orequal to about 75 mg/cm², less than or equal to about 70 mg/cm², lessthan or equal to about 65 mg-cm², less than or equal to about 64 mg/cm²,or less than or equal to about 62 mg/cm². Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 60 mg/cm² and less than or equal to about 100 mg/cm², greaterthan or equal to about 64 mg/cm² and less than or equal to about 75mg/cm²). Other values are also possible. The dirt holding capacity maybe determined by using a modified version of EN-13443-2 (2005) usingiso-fine test dust as described above except that (similar to theefficiency test) the flow rate of challenge solution may differ betweenflatsheet and cartridge elements. In the case of flatsheet, in somecases, a flow rate of a challenge solution may be 1 L/min (face velocityof 10.5 cm/min) whereas a flow rate of a challenge solution for acartridge element may be 15 L/min (face velocity of approximately 2.5cm/min).

In some embodiments, the pressure drop across the filter element at aflow rate of 15 liters per minute may be relatively low. For instance,in some embodiments, the pressure drop across the filter element mayless than or equal to about 5 kPa, less than or equal to about 4.8 kPa,less than or equal to about 4.5 kPa, less than or equal to about 4.2kPa, less than or equal to about 4 kPa, less than or equal to about 3.8kPa, less than or equal to about 3.5 kPa, less than or equal to about3.2 kPa, less than or equal to about 3 kPa, less than or equal to about2.8 kPa, less than or equal to about 2.5 kPa, less than or equal toabout 2 kPa, less than or equal to about 1.5 kPa, or less than or equalto about 1.5 kPa. In some instances, the filter element may have apressure drop of greater than or equal to about 1 kPa, greater than orequal to about 1.2 kPa, greater than or equal to about 1.5 kPa, greaterthan or equal to about 1.8 kPa, greater than or equal to about 2 kPa,greater than or equal to about 2.2 kPa, greater than or equal to about2.5 kPa, greater than or equal to about 2.8 kPa, greater than or equalto about 3 kPa, greater than or equal to about 3.2 kPa, greater than orequal to about 3.5 kPa, greater than or equal to about 3.8 kPa, orgreater than or equal to about 4 kPa. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 1 kPa and less than or equal to about 5 kPa, greater than orequal to about 1.5 kPa and less than or equal to about 4.5 kPa). Othervalues of pressure drop are also possible. The filter element pressuredrop can be measured using the standard NF X 45-302:2000. The pressuredrop was measured using 18 MegaOhm-cm deionized water with a flow rateof 15 liters per minute through the filter media.

In some embodiments, the pressure drop across the filter element at aflow rate of 20 liters per minute may be relatively low. For instance,in some embodiments, the pressure drop across the non-woven web may lessthan or equal to about 7 kPa, less than or equal to about 6.8 kPa, lessthan or equal to about 6.5 kPa, less than or equal to about 6.2 kPa,less than or equal to about 6 kPa, less than or equal to about 5.8 kPa,less than or equal to about 5.5 kPa, less than or equal to about 5.2kPa, less than or equal to about 5 kPa, less than or equal to about 4.8kPa, less than or equal to about 4.5 kPa, less than or equal to about4.2 kPa, less than or equal to about 4 kPa, less than or equal to about3.8 kPa, less than or equal to about 3.5 kPa, less than or equal toabout 3.2 kPa, less than or equal to about 3 kPa. or less than or equalto about 2.8 kPa. In some instances, the filter element may have apressure drop of greater than or equal to about 2.5 kPa greater than orequal to about 2.8 kPa, greater than or equal to about 3 kPa, greaterthan or equal to about 3.2 kPa, greater than or equal to about 3.5 kPa,greater than or equal to about 3.8 kPa greater than or equal to about 4kPa, greater than or equal to about 4.2 kPa, greater than or equal toabout 4.5 kPa, greater than or equal to about 4.8 kPa, greater than orequal to about 5 kPa, greater than or equal to about 5.2 kPa, greaterthan or equal to about 5.5 kPa, greater than or equal to about 5.8 kPaor greater than or equal to about 6 kPa. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto about 2.5 kPa and less than or equal to about 7 kPa, greater than orequal to about 3 kPa and less than or equal to about 6.5 kPa). Othervalues of pressure drop are also possible. The filter element pressuredrop can be measured using the NF X 45-302:2000. The pressure drop wasmeasured using 18 MegaOhm-cm deionized water with a flow rate of 20liters per minute through the filter media.

During use, the filter media mechanically trap contaminant particles onthe filter media as fluid (e.g., water) flows through the filter media.The filter media need not be electrically charged to enhance trapping ofcontamination. Thus, in some embodiments, the filter media are notelectrically charged. However, in some embodiments, the filter media maybe electrically charged. Charging of such filter media might beperformed by means of coating the media with ionic polymer.

Example 1

This example describes the structural characteristics of a calenderedfiber web and an uncalendered fiber web. The calendered fiber web had alower thickness, mean pore size, tensile elongation, and surface meanpore area as well as a higher number of fiber intersections per unitarea (a higher intersection density) compared to the uncalendered fiberweb.

Briefly, two meltblown fiber webs consisting of nylon 6 fibers having anaverage diameter of 4 m were formed by substantially the same process.One of the meltblown fiber webs was calendered. The meltblown fiber webwas calendered at a temperature 343.333° C., a pressure of 1.103161*10⁶Pa. and at a line speed of 6.096 m/min. Prior to calendering, the twomeltblown fiber webs had substantially the same properties. FIG. 2A is ascanning electron microscopy (SEM) image (micrograph) of theuncalendered fiber web and FIG. 2B is an SEM image of the calenderedfiber web. Table 1 shows the structural properties of the fiber webs.Regarding Table 1: Air permeability (Air perm); Mean flow pore size(MFP); Maximum pore size (Max pore); for thickness, 1 mil=0.0254 mm;machine direction (MD); 1 lb/in =175.127 N/m; 1 CFM=0.00047195 m³/s.

TABLE 1 Properties of Uncalendered and Calendered Fiber Webs SurfaceBasis Air Perm Max Mean Pore Intersection Tensile Meltblown WeightThickness (CFM) at MFP Pore Area Density lb/in Elongation % Fiber Web(g/m²) (mil) 125 Pa (μm) (μm) (μm²) (Ints/μm²) (MD) (MD) Uncalendered 235.5 180.8 20.2 42.2 65 0.0037 2.3 62.9 Calendered 22 3 93 14 43 13 0.0122.5 27

The calendered meltblown fiber web (e.g., FIG. 2B) had a highersolidity, smaller surface mean pore area, more fiber intersections perunit area, and a smoother surface than the uncalendered fiber web (e.g.,FIG. 2A).

Surface mean pore area was measured through scanning electron microscopyanalysis using DiameterJ, a plug-in for the ImageJ image analysissoftware. A Phenom desktop scanning electron microscope was used togenerate the micrographs. The micrographs were taken at a magnificationof 1200×. The electron acceleration voltage was 10 kV and backscatteredelectrons were used to create the micrographs. The cumulative area ofall pores in a micrograph was determined by converting the micrograph toa black-and-white image and calculating the area of the black pixels(representing at least a portion of a pore). Surface mean pore area wascalculated by dividing the cumulative pore area by the number of poresanalyzed. Solidity was estimated from the SEM images by subtracting thecumulative pore area from the total area of the image and dividing thedifference by the total area of the image, multiplying the result by 100for a solidity percentage.

The number of fiber intersections per micron squared was measuredthrough scanning electron microscopy analysis using DiameterJ. A Phenomdesktop scanning electron microscope was used to generate themicrographs. The micrographs were taken at a magnification of 1200×. Theelectron acceleration voltage was 10 kV and backscattered electrons wereused to create the micrographs. The total number of intersectionsbetween fibers at the surface of the layer was determined by countingthe intersections in a micrograph and dividing the number by the areacovered by the micrograph.

In addition, the calendered fiber web had a smaller mean flow pore size,thickness, and tensile elongation than the uncalendered fiber web.

Example 2

This example describes the structural and filtration properties of aflatsheet filter media including an efficiency layer formed on acalendered support layer and a flatsheet filter media including anefficiency layer formed on an uncalendered support layer. The filtermedia including the calendered support layer had better thickness andpore characteristics than the filter media including an uncalenderedsupport layer.

The filter media were formed by electrospinning a fiber web onto anuncalendered or calendered meltblown fiber web and laminating a secondmeltblown fiber web to the electrospun web. Lamination was performedwith a flatbed laminator at a temperature of 140.556° C., a pressure of55 psi (1 psi=6894.756 Pa), and a line speed of 30 feet/min (1foot=0.3048 m; 1 foot=12 inches (in)). All fiber webs contained nylonfibers. The second meltblown fiber web in filter media 1 and 2 differedonly with respect to basis weight.

Filter media 1 included an uncalendered meltblown fiber web having abasis weight of 30 g/m², an electrospun fiber web having a basis weightof 3 g/m² and an average fiber diameter of 120 nm, and a second(uncalendered) meltblown fiber web having a basis weight of 30 g/m². Theuncalendered meltblown fiber webs had a basis weight of 30 g/m², a meanflow pore size of 24 micron, max pore size of 55 micron, tensilestrength of 2.6 lb/in (1 lb/in =175.127 N/m), a tensile elongation of95.6%, a surface mean pore area of 65 μm², an intersection density of0.0037 ints/μm², and a thickness of 6.5 mil.

Filter media 2 included a calendered meltblown fiber web having a basisweight of 23 g/m², an electrospun fiber web having a basis weight of 1.6g/m² and an average fiber diameter of 120 nm, and a (uncalendered)meltblown fiber web having a basis weight of 23 g/m². The uncalenderedmeltblown fiber web had a basis weight of 23 g/m², a mean flow pore sizeof 20 micron, max pore size of 42 micron, tensile strength of 2.3 lb/in,a tensile elongation of 63%, a surface mean pore area of 65 μm², anintersection density of 0.0037 ints/μm², and a thickness of 5.5 mil. Thecalendered meltblown fiber web had a basis weight of 23 g/m², a meanflow pore size of 15 micron, max pore size of 45 micron, tensilestrength of 2.5 lb/in, a tensile elongation of 45%, a surface mean porearea of 13 μm², an intersection density of 0.012 ints/μm², and athickness of 3 mil. In Filter media 2, the structure was asymmetric: thesupport layer was calendered and had different properties than the thirdfiber web. Table 2 shows the structural and filtration properties of thefilter media. Microns=μm.

TABLE 2 Properties of the Filter Media Basis Air Perm Max Filter weightThickness (CFM) at Water perm MFP Pore Max media (g/m²) (mil) 2500 Pa(ml/min · cm² · psi) (μm) (μm) Pore/MFP Filter 62.5 9.4 10.5 2.6 0.162.4 15 media 1 Filter 48 5.6 30 5.2 0.28 0.6 2.14 media 2The weight of the support layer and cover layer were each around 23 gsm(g/m²). This was about 46 gsm total, plus 1.6 gsm of fine fiber(nanofiber web): 47.6 gsm, which was rounded to 48 gsm in Table 2.

As noted above, the electrospun fiber web in filter media 1 had agreater basis weight than the electrospun fiber web in filter media 2.It was found that even at higher basis weight of nanofiber, the maximum(max) pore size was much larger on an uncalendered support layer than ona calendered support layer.

As shown in Table 2, filter media 2 had a more homogeneous porestructure than filter media 1 and a higher water permeability. The ratioof maximum pore size to mean pore size for filter media 2 was seventimes smaller than the ratio for filter media 1.

In certain embodiments, the electrospinning process was therate-limiting step in the process of forming a filter media as describedherein. Without being bound by theory, by reducing the required mass offibers, one can increase the speed of the electrospinning process, thusincreasing the overall throughput of the process of forming a filtermedia. Without being bound by theory, using a calendered support layernot only allows a smaller amount of nanofiber to be used in theelectrospun layer, but also facilitates the production of a filter mediathat outperforms filter media having a support layer without theproperties of the calendered support layer.

Example 3

This example describes the structural and filtration properties of aflatsheet filter media including an efficiency layer formed on acalendered meltblown support layer and a flatsheet filter mediaincluding an efficiency layer formed on a calendered scrim/meltblownsupport layer. The filter media including the calendered meltblownsupport layer had a more homogeneous pore structure than the filtermedia including a calendered scrim/meltblown support layer.

The filter media were formed by electrospinning a fiber web onto acalendered meltblown fiber web or a calendered scrim/meltblown supportlayer and laminating a second meltblown fiber web to the electrospunweb. Lamination was performed with a flatbed laminator at a temperatureof 140.556° C., a pressure of 55 psi (1 psi=6894.756 Pa), and a linespeed of 30 feet/min (1 foot=0.3048 m; 1 foot=12 inches (in)). All fiberwebs contained nylon fibers. Filter media 2 included a calenderedmeltblown support layer and was formed as described in Example 2. Filtermedia 3 included a different support layer, the support layer includinga nylon spunbond scrim layer and a thin layer (10 gsm) (gsm=g/m²) ofmeltblown (e.g., comprising nylon 6) calendered together.

The second meltblown fiber web (e.g., layer 106 in FIG. 1A and layer 148in FIG. 1C) was the same in filter media 2 and filter media 3.

For filter media 3, the spunbond scrim fiber web was a Cerex fiber webhaving a basis weight of 20 g/m², a thickness of 4 mils, an airpermeability of 990 cfm (1 cfm=1 ft³/min=0.028317 m³/min) at 125 Papressure drop, and an average fiber diameter of 19 microns. Themeltblown fiber web in the support layer of filter media 3 had a basisweight of 11 g/m² (gsm), a thickness of 1.5 mil, and an average fiberdiameter of 3.6 microns. The 11 gsm meltblown fiber web was deposited ontop of the spunbond fiber web during the meltblowing process. After themeltblowing step, the meltblown fiber web and the spunbond fiber webwere calendered on top of each other to form the scrim/meltblown supportlayer. Properties of the calendered scrim/meltblown support layer wereas follows: basis weight of 31 g/m², thickness of 4.5 mil, airpermeability of 205 cfm measured at 125 Pa pressure drop, mean flow poresize of 21 micron and maximum pore size of 72 micron.

Table 3 shows the structural and filtration properties of the filtermedia.

TABLE 3 Properties of Various Filter Media Basis Air Perm Filter weightThickness at 125 MFP Max Pore Max FWHM 0.2 μm media (g/m²) (mil) Pa(CFM) (μm) (μm) Pore/MFP (μm) Efficiency Filter 48 5.6 1.5 0.28 0.6 2.140.035 98.9% ± 1.6% media 2 Filter 61 8.3 1.3 0.32 1.4 4.7 0.055   80% ±20.2% media 3

Filter media 2, having a calendered meltblown support layer with a meanflow pore size of 15 microns, outperformed filter media 3 (e.g., higher0.2 micron efficiency and higher air permeability, in Table 3), having acalendered scrim/meltblown support layer with a mean flow pore size of21 microns. Without being bound by theory, the difference in performancebetween filter media 2 and filter media 3 was at least because the poresize of the calendered scrim/meltblown support layer in filter media 3was larger than the pore size of the calendered meltblown backer (backeris also referred to herein as support layer) used in filter media 2.

Example 4

This example describes the filtration properties of standard 10″cartridge elements containing filter media, including a fibrousprotective layer and a fibrous efficiency layer on a calendered fibroussupport layer, compared to a commercial membrane filter. The filtermedia including fibrous layers had better efficiency, pressure drop, anddust holding capacity than the commercial membrane filter. The filtermedia were formed by electrospinning a fiber web onto a calenderedmeltblown fiber web (support layer) or meltblown/spunbond support layerand bonding a second meltblown fiber web to the electrospun web. Forfilter media 2 and filter media 3 that were used to form filter element2 and filter element 3, bonding involved lamination, performed with aflatbed laminator at a temperature of 140.556° C., a pressure of 55 psi,and a line speed of 30 feet/min. For filter media 4 and filter media 5that were used to form filter element 4 and filter element 5, bondinginvolved adhering the second meltblown fiber web, and the meltblown ofthe meltblown/spunbond support layer, to the electrospun fiber web usingan adhesive. An acrylic copolymer solution (adhesive) was applied byspray lamination to a surface of the meltblown of the meltblown/spunbondsupport layer before electrospinning the electrospun web onto thesupport layer; the acrylic copolymer solution was applied by spraylamination to a surface of the second meltblown fiber web beforeadhering the second meltblown fiber web to an exposed surface of theelectrospun fiber web. All fiber webs contained nylon fibers.

The support layer in filter media 3 and filter media 5 was as describedin Example 3; the support layer contained a meltblown fiber web asdescribed in Example 1 and a spunbond fiber web that were calenderedtogether prior to formation of the electrospun fiber web on thecalendered meltblown/spunbond fiber web. The support layer in filtermedia 2 and filter media 4 contained a calendered meltblown fiber web asin the calendered meltblown fiber web in filter media 2 in Example 2.

To form the standard 10″ cartridge elements, filter media were fed inroll format together with a layer of polypropylene scrim on the upstreamand two layers of polypropylene scrim on the downstream side, to a bladepleater to create 1.27 cm pleat height across the media and the scrimlayers. The pleated scrim-supported media was cut to an appropriatelength and seamed to form an open-ended cylinder. The pleated mediacylinder was inserted into a cartridge housing and enclosed by means ofheat sealing the end caps of the housing.

A commercial membrane filter served as the control.

The control sample, characterized in Table 4, was a commercial Nylon 6,6hydrophilic membrane with an absolute rating of 0.45 micron.

TABLE 4 Properties of commercial Nylon 6,6 membrane Air Perm Basis (CFM)Filter weight Thickness (e.g., MFP Max Pore Max FWHM 0.2 μm media (g/m²)(mil) at 125 Pa) (um) (um) Pore/MFP (um) Efficiency Commercial 0.30.7 >2.7 0.36-0.42 31.2% ± 20% membrane

As shown in FIGS. 3A-3D, regardless of the calendered support layerutilized (a calendered meltblown fiber web in filter element 2 andfilter element 4, or a meltblown/spunbond support layer in filterelement 3 and filter element 5) or the bonding technique (heatlamination in in filter element 2 and filter element 3, or adhesivebonding in filter element 4 and filter element 5), the filter elementscontaining filter media including fibrous layers had a higher 0.2 micronparticulate efficiency, a better 0.3 micron particulate efficiency, ahigher dust holding capacity (DHC) (and accordingly a higher lifetime),and a lower pressure drop at 15 lmp than the commercial membrane filter.

The filter elements 2, 3, 4, and 5 had substantially the same filtrationefficiencies as filter media 2, 3, 4, and 5 respectively, which suggeststhat the filter media 1) maintained their uniformity of pore sizedistribution in the filter elements; and 2) were generally able towithstand the stresses of the pleating process to form filter elementsfrom the corresponding filter media without sacrificing filtrationefficiency (e.g., filter elements 3, 4, and 5 FIG. 4). By contrast,efficiency losses after pleating are often observed for other filtermedia. In addition, in cartridge (filter element) form, the filterelements 2, 3, 4, and 5 had a significantly higher dust holding capacitythan that in flatsheet (disk) form (for corresponding filter media 2, 3,4, and 5) (e.g., FIG. 5).

Example 5

This example shows the filtration properties of a filter media 6,including a meltblown support layer and a poly(ether sulfone) nanofiberlayer (efficiency layer). The support layer was a pre-calenderedpoly(butylene terephthalate) (PBT) meltblown layer with a basis weightof 40 g/m². The nanofiber layer (efficiency layer) was a poly(ethersulfone) (PES) nanofiber layer having a basis weight of 5 g/m² and anaverage fiber diameter of 120 nm, directly adjacent to and formed on thePBT meltblown by electrospinning to form a PBT/PES construct. ThePBT/PES construct was laminated with a second PBT meltblown layer (basisweight 30 g/m²), positioned directly adjacent to the other side of thenanofiber layer to form a laminated composite. Lamination settings were165.6 degrees Celsius, 550 kPa, dwell time 17 seconds. The basis weightof the resulting filter media was 75.3 gsm, thickness 0.018 cm, meanflow pore size 0.22 microns, max pore size 1.15 microns, ratio (max poresize)/(mean flow pore size) 5.16.

The laminated composite was subsequently plasma-treated using RFChemical Vapor Deposition with oxygen gas in order to create ahydrophilic media (filter media 9) fully water-wettable from its top tobottom surface. This media is compared with commercially availablemicrofiltration PES membranes in Table 5.

TABLE 5 Properties of Various Filter Media Basis Max Water 0.2 μm Filterweight Thickness Air Perm ** MFP Pore Max permeability Efficiency media(g/m²) (mil) (CFM) (μm) (μm) Pore/MFP (ml/min · cm² · psi) (%) filter 740.2 13.2 0.2 1.05 2.57 2.7 90 media 6 *Membrane 31 4.7 13.5 0.37 0.852.3 0.7 48 PES - 0.45 μm Vendor1 *Membrane 0.9 37 PES - 0.45 μm Vendor2*Membrane 42.6 5.5 14.6 0.36 0.66 1.85 1.2 20 PES - 0.45 μm Vendor2*Membrane 0.32 0.42 1.32 0.5 55 PES - 0.2 μm Vendor3 *Commerciallyavailable microfiltration PES membranes ** at 2,500 Pa

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

What is claimed is:
 1. A filter media comprising: a first fiber webcomprising first fibers, wherein the first fibers comprise electrospunfibers and have an average diameter of less than or equal to 0.5microns, wherein the first fiber web has a thickness of less than orequal to 200 microns; a calendered fiber web directly adjacent to thefirst fiber web; and a third fiber web bonded to the first fiber web;wherein the filter media has a maximum pore size of greater than orequal to 0.1 microns and less than or equal to 2.5 microns and a fullwidth at half maximum of a pore size distribution of less than or equalto 0.2 microns.
 2. A filter media comprising: a first fiber webcomprising first fibers having an average diameter of less than or equalto 0.5 microns, wherein the first fibers comprise electrospun fibers andwherein the first fiber web has a thickness of less than or equal to 200microns; a calendered fiber web directly adjacent to the first fiberweb; and a third fiber web bonded to the first fiber web; wherein thefilter media has a maximum pore size of greater than or equal to 0.1microns and less than or equal to 2.5 microns, a full width at halfmaximum of a pore size distribution of less than or equal to 0.2microns, and a ratio of maximum pore size to mean pore size of less thanor equal to 5.0.
 3. A filter media comprising: a first fiber webcomprising first fibers, wherein the first fibers comprise electrospunfibers and have an average diameter of less than or equal to 0.5microns, wherein the first fiber web has a thickness of less than orequal to 200 microns; a second fiber web directly adjacent to the firstfiber web, wherein the second fiber web has a dry tensile strength inthe machine direction of greater than or equal to 1 lb/in and less thanor equal to 35 lb/in, a dry tensile elongation in the machine directionof greater than or equal to 10% and less than or equal to 60%, and amean pore size of greater than or equal to 1 micron and less than orequal to 30 microns; and a third fiber web bonded to the first fiberweb; wherein the filter media has a maximum pore size of greater than orequal to 0.1 microns and less than or equal to 2.5 microns, and a fullwidth at half maximum of a pore size distribution of less than or equalto 0.2 microns.
 4. A filter media comprising: a first fiber webcomprising first fibers, wherein the first fibers comprise electrospunfibers and have an average diameter of less than or equal to 0.5microns, wherein the first fiber web has a thickness of less than orequal to 200 microns; a second fiber web directly adjacent to the firstfiber web, wherein the second fiber web has a surface mean pore area ofgreater than or equal to 2 μm² and less than or equal to 50 μm², anintersection density of greater than or equal to 0.005 intersections/μm²and less than or equal to 0.025 intersections/μm², and a mean pore sizeof greater than or equal to 1 micron and less than or equal to 30microns; and a third fiber web bonded to the first fiber web; whereinthe filter media has a maximum pore size of greater than or equal to 0.1microns and less than or equal to 2.5 microns, and a full width at halfmaximum of a pore size distribution of less than or equal to 0.2microns.
 5. The filter media of claim 1, wherein the first fiber web hasa basis weight greater than or equal to 0.5 g/m² and less than or equalto 10 g/m².
 6. The filter media of claim 1, wherein the first fiber webcomprises first fibers having an average diameter of greater than orequal to 0.05 microns and less than or equal to 0.5 microns.
 7. Thefilter media of claim 1, wherein the first fiber web is non-calendered.8. The filter media of claim 1, wherein the calendered fiber webcomprises a meltblown fiber web.
 9. The filter media of claim 1, whereinthe calendered fiber web further comprises a spunbond layer.
 10. Afilter media of claim 3, wherein the third fiber web has an averagefiber diameter greater than that of the first fiber web and less thanthat of the second fiber web.
 11. A filter media of claim 1, wherein thethird fiber web has an average fiber diameter greater than that of thefirst fiber web and less than that of the calendered fiber web.
 12. Thefilter media of claim 1, wherein the third fiber web comprises ameltblown fiber web.
 13. The filter media of claim 1, wherein the thirdfiber web has a maximum pore size of greater than or equal to 20 micronsand less than or equal to 70 microns.
 14. The filter media of claim 1,wherein the filter media has a mean flow pore size of less than or equalto 1 micron.
 15. The filter media of claim 1, wherein the filter mediahas an air permeability of greater than 0.5 CFM and less than or equalto 10 CFM for a pressure drop of 125 Pa.
 16. The filter media of claim1, wherein the filter media has a thickness of greater than or equal to100 microns and less than or equal to 400 microns.
 17. The filter mediaof claim 1, wherein the filter media has a tensile strength in themachine direction of greater than or equal to 1 lb/in and less than orequal to 150 lb/in.
 18. The filter media of claim 1, wherein the filtermedia has a tensile elongation in the machine direction of greater thanor equal to 1% and less than or equal to 30%.
 19. The filter media ofclaim 1, wherein the filter media has a basis weight of greater than orequal to 40 g/m² and less than or equal to 80 g/m².